Shepsle Laver Events Equilibria

Events Equilibria and Government Survival

Michael laver Kenneth A Shepsle

American Journal of Political Science Vol 42 No 1 (Jan 1998) pp 28-54

Stable URL

httplinksjstororgsicisici=0092-58532819980129423A13C283AEEAGS3E20CO3B2-D

American Journal of Political Science is currently published by Midwest Political Science Association

Your use of the JSTOR archive indicates your acceptance of JSTORs Terms and Conditions of Use available athttpwwwjstororgabouttermshtml JSTORs Terms and Conditions of Use provides in part that unless you have obtainedprior permission you may not download an entire issue of a journal or multiple copies of articles and you may use content inthe JSTOR archive only for your personal non-commercial use

Please contact the publisher regarding any further use of this work Publisher contact information may be obtained athttpwwwjstororgjournalsmpsahtml

Each copy of any part of a JSTOR transmission must contain the same copyright notice that appears on the screen or printedpage of such transmission

The JSTOR Archive is a trusted digital repository providing for long-term preservation and access to leading academicjournals and scholarly literature from around the world The Archive is supported by libraries scholarly societies publishersand foundations It is an initiative of JSTOR a not-for-profit organization with a mission to help the scholarly community takeadvantage of advances in technology For more information regarding JSTOR please contact supportjstororg

httpwwwjstororgTue Feb 12 050529 2008

Events Equilibria and Government Survival Michael Laver Trinity College Dublin Kenneth A Shepsle Harvard University

Theory A game-theoretic model of government formation yields an equilibrium government the robustness of which may be explored by subjecting it to exogenous shocks This permits an examination of government durability and survival in a cruel political world Hypotheses The vulnerability of a government to exogenous shocks depends upon the nature of the shock A government may be quite resistant to some classes of shock while it is highly vulnerable to others Methods Game-theoretic analysis yields equilibrium results A simulation technology is crafted which allows us to subject this equilibrium to perturbations of its underlying parameters (much in the spirit of wind-tunnel experiments in engineering) Results The technology does indeed allow the systematic examination of well-defined cases We find for the case of two European governments in the 1980s and 1990s that they differ considerably in their vulnerability to exogenous shocks

Introduction In order to understand the workings of parliamentary government one

must determine what it takes for a government to survive in a cruel political world In order to do this we must understand the circumstances that led to a particular government taking office in the first place and the circumstances in which this government would be replaced by some alternative This con- centrates our attention on how radically circumstances must change before a government falls and is replaced If a government can survive dramatic changes in its political environment while still managing to hold on to the reins of power we think of it as relatively stable If a government cannot survive even quite small changes to the environment in which it originally took office we think of it as being relatively unstable

This paper is concerned with government survival in parliamentary democracies exploring factors that might destabilize equilibrium governments This is not just an abstract academic problem In practical political terms the survival potential of any real-world government is of obvious interest to the wide range of actors who must deal with it These include among many others opposition parties citizens interest groups revolution-

This paper was originally prepared for the Annual Meeting of the American Political Science As- sociation San Francisco 1996 We are grateful for the comments there from Sven Feldmann and Barry Weingast For programming assistance we thank Paul Doyle We also gratefully acknowledge the comments of three anonymous referees

American Journal of Political Science Vol 42 No 1 January 1998 Pp 28-54 O 1998 by the Board of Regents of the University of Wisconsin System

29 EVENTS EQUILIBRIA AND GOVERNMENT SURVIVAL

aries investors foreign governments and international organizations For both practical and theoretical reasons therefore one of the most important applications of any model of parliamentary politics is to analyze the ability of an incumbent government to survive changes in its political environment

The discussion that follows is developed in several stages First we review briefly the main themes in the surprisingly small political science literature on government survival concluding that what is missing from this literature is a theoretical account of what it takes to disequilibrate a government or put differently why one equilibrium government should be replaced by another Second we propose various ways in which recent theoretical developments might be elaborated into a more comprehensive approach to the analysis of government survival Third we propose a simulation technology that allows substantive progress to be made in this analysis despite major analytical puzzles that remain to be solved Fourth we use the technology we develop to explore the survival potential of two particular real-world governments

Government Survival The Story So Far Considering that it is such a self-evidently important topic government

survival in parliamentary systems has been rather neglected by political sci- entists The most striking evidence of this neglect is that the first book-length treatment of the subject appeared only in 1994 (Warwick 1994) Fortunately Paul Warwick who has been one of the most consistent and innovative con- tributors to the literature so far provides an excellent review of the literature on government survival and it would be pointless to repeat this here A simple sketch will suffice

Most previous discussions of government survival have shared two striking features They have been heavily inductive in their logic and they have concentrated upon government duration as the key variable to be ex- plained The government survival debates as Warwick aptly titles his review have essentially concerned two issues The first has been the identity of independent variables to be included in multivariate statistical analyses of government duration The second has been the determination of the most appropriate statistical model for conducting such an analysis

The debate over the most appropriate statistical model for analyzing government durations has been unusual and interesting in political science terms Rather than being an arcane discussion on statistical technique among methodologists as it might appear on the surface it has actually been a debate on how best to conceive of government stability and the processes that underlie this

An earlier review can be found in the chapter on government stability in Laver and Schofield (1990)

30 Michael Laver and Kenneth A Shepsle

On the one hand is a group of deterministic models that implicitly assume the durability of a particular government to be an attribute it pos- sesses one conditioned by features of the government fixed at the time of its formation (Examples of this attributes approach include Sanders and Herman 1977 Strom 1985 Taylor and Herman 1971 Warwick 1979) On the other hand is a stochastic model generated by Browne Frendreis and Gleiber (1984 1986 1988) for whom governments exist in a world of criti-cal events each event having some probability of destroying the government in a process that is essentially random The methodological debate arises because if this events approach to government stability is accepted then it is quite inappropriate to analyze cabinet durations using OLS regression models (which apart from anything else often predict negative government durations for feasible configurations of parameter values)

Browne Frendreis and Gleiber stated what with the benefit of hindsight was an extreme version of the events approach that implied government durations were entirely a product of the flow of critical events so that no government was inherently more durable than any other Since the deterministic attributes approach had achieved some empirical success in analyzing government durations this did not seem entirely plausible King et al (1990) showed that it is possible to specify a statistical model derived from event history analysis that reconciles a view that government survival was an inherently stochastic process one in which real-world governments exist in a flow of potentially fatal critical events with a view that some governments have attributes that make them inherently more stable than others The most obvious attribute that can enhance government stability is a legislative majority but several other attributes do improve empirical accounts of government duration

Subsequently Warwick (1994) developed and enhanced this unified approach The results of his extensive research in this tradition are reported and discussed in his book and this work now represents the prevailing orthodoxy in empirical accounts of government survival It remains characterized by an inductive approach The style of analysis is to identify a set of independent variables with prima facie relevance to government duration The variables are then operationalized and an empirical analysis is performed using an event history model Causal modeling is essentially inductive The result of the empirical analysis is a best-fitting statistical model

The Way Forward The Need for a Theory of Government Survival

What is missing from these orthodox accounts of government stability is a theoretical model of what causes one government equilibrium to be replaced with an alternative Without such a model it is not possible to pro-

EVENTS EQUILIBRIA AND GOVERNMENT SURVIVAL 31

vide a comprehensive account of the survival of governments in parliamentary democracies

It should hardly be necessary to go into much detail on why a purely empirical account of government survival will always leave us short of a theoretical explanation for what is going on An empirical account identifies factors associated with government survival or duration These regularities must be embedded in a model in order to ascertain the mechanisms by which these factors do in fact translate into longer lasting governments or higher probabilities of survival Purely empirical accounts in other words are the stuff of Humes constant conjunction not of his necessary connection The latter is required to know why particular factors are associated with government survival

Actually the events theorists did have an explicit model of government equilibrium albeit a very simple one In some ways it is unfortunate that their work has been presented within the prevailing orthodoxy as a methodological argument for a change in statistical method from OLS regression to event history analysis Epistemologically it is much more than this The theoretical contribution made by Browne Frendreis and Gleiber was to argue that every government is an equilibrium government in some sense at the moment of its formation and that the duration of this government can be modeled by treating it as if it is forced to survive bombardment by critical events any one of which has some probability of destroying the government equilibrium They did not concern themselves with why the original government was in equilibrium But their argument implies that it must have been the equilibrium outcome of some unmodeled process since it was the government that did indeed form Of course this means that Browne Frendreis and Gleiber are utterly silent on what follows the disequilibration reflected in a government defeat For them in effect the unmodeled government formation process then generates a new equilibrium which they take as it comes and which is immediately subjected to relentless bombardment by critical events

It seems to us that the notion that governments must survive bombardment by critical events is very persuasive both substantively and epistemologically We argue in this paper that the way forward is not to continue the inductive search for stability-inducing attributes but rather is to derive a rigorous theoretical model that builds upon and extends the idea that a government must be in equilibrium at the moment of formation by virtue of the simple fact that it formed

Public Opinion Shocks in Three-Party Legislatures The model we have in mind sees an equilibrium government as the out-

come of the strategic choices faced by the people whose actions result in its


formation A change in the government equilibrium the end of one government and the beginning of another must therefore be the result of a change in the political incentives for one or more pivotal actors leading them to change strategies in such a way as to create a new government equilibrium

One recent theoretical exploration has developed precisely along these lines (Lupia and Strom 1995) They consider a status quo government in the aftermath of a particular type of critical event one that changes the electoral expectations of key actors We might think of this as apublic opinion shock This shock changes the political environment in which the status quo government must exist with the result that some actors may change their minds about whether or not to bring down the government Lupia and Stroms cen- tral argument is developed for a three-party legislature and derives from the plausible assumptions that first bringing down a government has opportunity costs for government members (the loss of the remainder of their consti- tutionally mandated term of office) while second both fighting elections and getting involved in coalition renegotiations have transaction costs for all involved

Driven by these assumptions their model shows that government coalition parties who find as a result of a public opinion shock that they stand to gain seats at the next election (were one held immediately) may nonetheless have an incentive either to continue to accept the status quo or to renegoti- ate a new coalition agreement without an election rather than to force an election and thereby realize anticipated electoral gains This result is interesting because it runs counter to what on the face of things might seem the common-sense assertion that coalition members bring down governments when they anticipate electoral gains (Grofman and van Roozendaal 1994)

A further important insight emerging from the Lupia-Strom model is that as a consequence of the declining opportunity costs of a government collapse as any administration steadily approaches the end of its constitu- tionally imposed maximum term the likelihood of the same event destabilizing the government increases throughout the life of the government This provides a theoretical justification for the empirical finding of a rising hazard rate-that other things being equal the probability of government ter- minations appears to increase throughout a governments term of office (Warwick 1994)

There are several ways in which the Lupia-Strom model could be extended to incorporate interesting features of the government termination process One is the strategic asymmetry that exists in many countries by virtue of the fact that only the Prime Minister (and hence the PMs party) has the constitutional power to request a dissolution of the legislature the opposition parties and the other government party or parties do not Thus a majority coalition consisting of opposition parties and non-PM government parties can make the PMs life a misery to be sure But they cannot directly

EVENTS EQUILIBRIA AND GOVERNMENT SURVIVAL 3 3

impose a dissolution on a PM who stares them down In order to force a dissolution a majority coalition excluding the PMs party must bring down the government install a rival PM and then have him or her seek to dissolve the legislature In other countries such as Norway Finland and Switzerland the government has very little strategic control over the timing of elections The Lupia-Strom model could be extended in interesting ways to capture these variationsa2

Another possibility that is not fully covered by the Lupia-Strom treatment of opportunity costs arises if government parties form the view after a public opinion shock that potential electoral gains accruing to them are likely to continue to be available for some time in the future In this event government parties need not incur the opportunity costs of bringing down the government and having an immediate election but can effectively bank their public opinion windfall with a view to forcing an election and cashing it in at some future date thereby extending their expected tenure of office

A further issue is the restriction of the Lupia-Strom model to three-party systems They make the claim in a footnote that we can use our three-party model to explain the dynamics of an n-party bargaining situation by assuming that at least one of our parties is actually a protocoalition This expansion is problematic only to the extent that the unitary-actor assumption does not carry over well in the case of a protocoalition (Lupia and Strom 1995 663n) However it is not at all self-evident that the complex proofs tendered by Lupia and Strom would go through in a situation in which one party was in fact a protocoalition of two or more parties each with different pref-erence schedules each affected differently by the public opinion shock each negotiating separately with other actors and each capable of choosing dif-ferent coalition partners in any renegotiation Suppressing all of that political action by imposing the unitary actor assumption on a protocoalition does seem impla~sible ~

These are all matters for a second-generation model however There is no doubt that Lupia and Strom have made significant progress in under- standing the impact of public opinion shocks on coalitions in three-party legislatures This is a very important first step along the road to a fuller theoretical account of government survival allowing us to see that it is indeed possible to model the impact of events on government survival in a logically rigorous manner

2For further details on confidence votes and parliamentary dissolution see Huber (1995 1996) Country-by-country detail on these matters in tabular form is found in Gallaher Laver and Mair (199530)

3We should also note that in other contexts (for example entry models of electoral competition) n = 3 parties is not a good proxy for generalizing to n gt 3 parties Equilibrium may exist for the latter circumstance but not for the former For details see Shepsle (1991)


A Broader Treatment of Critical Events The next steps along this road will involve developing more convincing

accounts of n-party legislatures and dealing with the impact of critical events other than public opinion shocks One relevant approach has recently been suggested by Laver and Shepsle (1996) elaborating a model first put forward as a result of independent work by Laver and Shepsle (1990) and Austen-Smith and Banks (1990) They develop a game-theoretic model of equilibrium government that can be applied to a legislature with any number of parties The capacity of any particular equilibrium government to survive perturbations of key model parameters can then be explored

Laver and Shepsles portfolio allocation model of equilibrium government in parliamentary democracies is based upon a set of assumptions that can of course be debated bur which we will not debate here in the interests of arriving quickly at a model of government survival Their core assumption is that governments are fundamentally characterized by the particular allocation of key cabinet portfolios among parties This is because cabinet ministers in practice have considerable influence over policy outputs in areas under the jurisdiction of their portfolios The partisan allocation of portfolios in this way forms the basis of forecasts about the policy output of any given government Thus health policy is heavily conditioned by the partisan political agenda of the minister of health defense policy by the views of the political party of the minister of defense and so on Equilibrium governments in the Laver-Shepsle model emerge in several different ways Here we focus on one form of equilibrium The dimension-by-dimension median cabinet is the cabinet in which each key portfolio is allocated to the party with the median legislator on the policy dimension characterizing the jurisdiction of that portfolio It is an equilibrium if it has an empty winset-that is if no other portfolio allocation is preferred to it by a parliamentary ma j~ r i t y ~

Laver and Shepsle explore the issue of government survival by first using their model to identify equilibrium cabinets and then investigating the sensitivity of such equilibria to perturbations in model parameters Each model parameter in effect identifies a particular class of critical events that have an explicit theoretical bearing on the stability of government equilibria One class is the sort of public opinion shock that forms the basis of the Lupia- Strom model Other things being equal an equilibrium cabinet that ceases to be in equilibrium as a result of relatively small perturbations in model param-

4Surely majorities will prefer many policies to the one associated with a putative equilibrium cabinet This is the well-known fact of life about majority rule institutions in multidimensional contexts The Laver-Shepsle claim is that it is entirely more likely to find that the dimension-by-dimension median cabinet is preferred by a majority to every other cabinet (each of which is associated with a forecast policy that some majority likes less than the multidimensional median policy)


eters is forecast to be less likely to survive in the real world than an equilib-rium cabinet that requires larger perturbations in the same parameters before it ceases to be an equilibrium Statistically a higher proportion of critical events should destabilize the former than the latter government

This way of doing things thus builds upon both the purely stochastic events approach used by Browne Frendreis and Gleiber and the deduc-tive approach used by Lupia and Strom It involves constructing an explicit deductive model of parliamentary government then unpacking the substan-tive implications of this model for government survival according to the epistemological assumptions of the events a p p r ~ a c h ~In effect we are recommending a form of sensitivity analysis in which we ask whether a par-ticular configuration of parameters sustaining an equilibrium is robust to shocks and if so then how robust

What Do Shocks Shock We have just argued that the best way to model the government survival

process is to take a model of government equilibrium and analyze the impact on equilibrium of shocks to key parameters This means that our account of government survival will be driven by the variables assumed to condition government equilibrium The key variables used by the portfolio allocation model (and of course by many other extant or conceivable models) to iden-tify equilibrium governments are

party positions on key policy dimensions party specific saliency weights attached to these dimensions the distribution of seats among parties the legislative decision rule used to sustain a government in office

Change in the values of any one of these variables may according to the portfolio allocation model destabilize an existing equilibrium govern-ment The variables identified by this model are hardly exotic however and have an important role in most accounts of government formation that take party policy seriously They are thus likely to figure in any compre-hensive account of government survival These variables thus help us to specify classes of critical event that have a bearing upon government sur-vival Any critical event that has an effect on government survival that we

5Animportant point to make at this stage is that this way of using a model of government equi-librium to generate a model of government survival is generic-the methodology does not require any particular model of government equilibrium Government survival could be analyzed using any model generating a clear specification of an equilibrium government and the parameters that under-pin this Given any such model the underlying technique of investigating the sensitivity of particu-lar government equilibria to the perturbation of key model parameters could be employed


Table 1 Classification of Critical Events

Model parameter perturbed Type of critical event

Party ideal points Policy shock

Party-specific dimension weights Agenda shock

Expected seat distribution in immediate election Public opinion shock

Effective majority required for government survival Decision rule shock

can explore analytically must do so because it causes a disequilibrating shock to the value of one of the basic model variables These are summa- rized in Table 1

Events That Shock Party Policy Positions Policy Shocks The original Laver-Shepsle (1996) discussion of cabinet stability con-

centrated on shocks to the matrix of distances between party ideal points Such shocks were used to model generic critical events on the grounds that many critical events have the effect of changing how the parties feel about each others policy commitments thus changing the matrix of inter- party distances

However an important matter that is brought into focus by Lupia and Stroms more explicit modeling of the impact of a particular type of shock concerns the precise substantive meaning of modeling shocks by perturbing party ideal points After all party ideal points represent the tastes of parties which Laver and Shepsle take in all other parts of their argument to be primitives not strategic variables Even assuming party ideal positions on a given set of issues to reflect fundamental tastes however it is possible to conceive of ways in which party positions on policies within the jurisdiction of various cabinet portfolios might change over time This is because politi- cians and parties are agents for constituencies in the broader polity Party ideal points reflect preferences induced by this agency relationship And constituency interests (the principles of the principals so to speak) surely change as events impinge upon markets factors of production income and many other things besides

Thus foreign policy positions for example are of their very essence open to the impact of exogenous shocks The Berlin Wall is torn down civil war flares up in Bosnia or Rwanda Britain dispatches a task force to retake the Falkland Islands from Argentina Few of these events could reliably have been foreseen yet each creates a need for government and opposition parties in many other countries to assess their present policy position or in some instances to take altogether new policy positions Unanticipated events-


sudden runs on foreign currencies unexpected major bankruptcies-can ob-viously have similar effects on economic policy Indeed it is not hard to think of examples of the way in which this type of policy shock can stimu- late policy reconsideration and indeed add new issues to any important policy jurisdiction In this way events can constitute the exogenous shocks that perturb party positions in major policy jurisdictions

Events that Rearrange the Policy Agenda Agenda Shocks A second class of political event identified in Table 1 may disturb an

equilibrium by affecting the relative salience of key policy jurisdictions Such events do not effect a reconsideration of specific issues positions and thus do not shock party ideal points Rather they affect the relative importance of policy jurisdictions Even after the Balkans conflict has become part of the foreign policy issue bundle for example and even if party positions on it have done all the adjusting they are going to do particular dramatic events and atrocities in Bosnia may raise the overall profile of foreign policy forcing it higher up the political agenda We might therefore think of these events as agenda shocks

Each political actor (or political party if we use the assumption of parties as unitary actors) gives a relative weight to each policy jurisdiction These weights may well be very different for different parties in the same ~ y s t e m ~The perceived aggregate policy distance between two parties is then a function of policy distances between them on each key policy dimension weighting the distance on each dimension for each party by the party- specific dimension eight^ This of course creates a situation in which it is likely that Party As view of the distance between Party A and Party B will differ from Party Bs view of precisely the same thing since each applies different weights to their differences on each dimension

We can think of agenda shocks as changing party-specific dimension weights This allows for the possibility that an event can change how Party A feels about Party B in a way that is different from the change in how Party B feels about Party A ~ Imagine two parties one a social democratic party and one a fundamentalist religious party The social democratic party gives a much higher weight to the economic policy dimension than to the social1 moral policy dimension the fundamentalist religious party does the reverse An example of an agenda shock might be a supreme court decision unexpectedly changing abortion law This would be a much bigger deal for the

6Empirical evidence of just how different party-specific dimension weights can be was col- lected by Laver and Hunt (1992)

This is it will be a function of the salience-weighted Euclidean distance 8 ~ o rprecisely this reason it is difficult to illustrate the impact of shocks to party-specific di-

mension weights in a simple diagram


fundamentalist religious party than for the social democratic party Even though the party positions on abortion would not change the increased salience of the abortion issue for the religious party would create a situation in which it perceived a widening gap between it and the social democratic party a change that might be considerably less visible to the latter If the two parties happened for some reason to be in coalition together the relative incentives for each to end the arrangement may change as a result of this agenda shock despite the fact that their policy positions remained the same

Events that Shock Expected Election Results Public Opinion Shocks Lupia and Strom base their model of government survival on the impact

of an event that affects commonly held expectations concerning the outcome of a potential election (1995648)-we will call these public opinion shocks Parties in the Lupia-Strom model are assumed to care about con- trolling seats in parliament (1995652) Indeed the payoffs they assume for each party derive from a simple additive function of legislative seat share and coalition payoff (1995 653)9 Thus an event that affects the expected result of the next election for example an unexpected opinion poll finding potentially affects the incentives of various parties to destroy the government even if the event is expected to result in no change whatsoever to the set of winning coalitions which we refer to as the decisive structure1deg

In the three-party world of the Lupia-Strom model of course almost every public opinion shock will leave unchanged the decisive structure anticipated after the next election The only decisive structure with coalition potential makes any two parties capable of forming a winning coalition the only type of shock to the decisive structure that can change this is one big enough to give a single party an overall majority Thus if Lupia and Strom did not assume parties value legislative seat shares intrinsically and thus re- negotiate the coalitions to which they belong so as to realize the utility gains deriving from changes in forecasts about seat shares then the only time anything would happen in their model is when a big enough public opinion shock arrived to offer one party the prospect of a single-handed legislative majority

Laver and Shepsle in contrast regard the legislative seat share as an entirely instrumental concern for each party important only to the extent it

gLupia and Strom actually conceptualize party objective functions in a more general fashion so that in their model shocks also affect things other than expected election results Nevertheless their examples and running commentary focus primarily on the latter so we think of theirs mainly as an analysis of public opinion shocks

OThat is since parties care about seat share they may he motivated to bring down a sitting government and provoke new elections in order to capture a seat-share dividend even if such changes in seat shares leave the original decisive structure intact


affects the party composition of the government that is forecast to result from a particular seat distribution This implies that the only public opinion shocks that can have an effect on model predictions are those that change the decisive structure Public opinion shocks thus have very discontinuous effects Some large shocks will have no effect whatsoever but as the seat distribution moves close to a threshold quite small shocks can have quite big effects In the three-party case for example if three parties each have 33 seats in a 99 seat legislature only whopper public opinion shocks big enough to lead to the prediction that one party will gain at least 17 seats to give it an overall majority will change the parties calculations In another 99 seat legislature in which two parties have 49 seats and the third party has one seat a teeny-weeny shock forecast to result in a single seat gain by one of the two big parties would have the same destabilizing effect It is as well to be aware therefore that our own exploration of government survival is concerned solely with incentives arising from the composition of the government rather than from any intrinsic satisfaction associated with doing well in legislative elections

We should further note that we assume public opinion shocks to affect the calculations only of parties in a position to bring about an immediate election As we pointed out earlier when discussing the Lupia-Strom account of public opinion shocks there is an important asymmetry in the making and breaking of governments that we must consider if we are to develop a convincing account of the impact of public opinion shocks on government stability Not all parties are equally able to force an election when the circumstances favor them Opposition parties are typically quite unable to force an election when as is very often the case they do well in public opinion polls during the lifetime of the government In fact it is usually the case that only the Prime Ministers party can directly impose an early election so that the only public opinion shocks likely unambiguously to result in an election are those that improve for the PMs party the government equilibrium anticipated to result from a forced election12 Since the PMs party is already in government and already controls the Prime Ministership the only real strategic benefit of an early election in this sense arises from an anticipated result that allows the PMs party to get rid of some or all coalition partners and form a new government in which it controls more key portfolios

As the number of parties increases the number of possible decisive structures goes up at a very rapid rate and the probability that a small change in seat shares will change the decisive structure increases accordingly The difference between shocks to seat shares and shocks to decisive structures thus narrows as the number of parties increases

I20ne bit of ambiguity remains It is possible that the PMs party could elicit agreement from other government parties to reshuffle some of the portfolios effectively impounding the import of the public opinion shock while avoiding the necessity of holding an early election


Government parties other than the PMs party may however have the indirect power to force an election If a public opinion shock makes a non- PM government party very strong13 then it can resign form an alternative administration in which it controls the prime ministership then force an election from this position Opposition parties would facilitate this since they too favor a minority government run by the non-PM government partner l4 Thus public opinion shocks making a non-PM government partner very strong are also destabilizing according to the portfolio allocation model

Events that Shock the Decision Rule While every aspect of the institutional environment of parliamentary

democracies is of course an endogenous product of politics in the long term it is conventional to treat certain institutional features as being fixed exog- enously within the timescale of the process under consideration When looking at the making and breaking of governments analysts almost always take the legislative decision rule - typically majority voting - to be fixed in the sense that changing the decision rule is not considered to be a feasible part of the process of making or breaking a government Both the Lupia-Strom and the Laver-Shepsle accounts follow this convention Looking at things in more general terms however it may happen that the majority decision rule underpinning the formation of a particular equilibrium government may ef-fectively (if not formally) be changed during the lifetime of that government potentially undermining its stability

We know of no real-world situation in which the majority rule for votes of confidencelno confidence in the government has been abandoned formally However some constitutions do require qualified majorities in parliament for certain policy changes for example those involving alterations of the constitution A government that forms when no constitutional issue is on the agenda or foreseen may in such cases be destabilized if a shock not only causes such an issue to emerge out of the blue but also is of sufficient importance that the government cannot govern effectively if it cannot make the necessary constitutional revision It may be in equilibrium given the majority decision rule but out of equilibrium given the qualified majority rule implied if it is to continue effectively in office The reemergence of commu- nal strife in Belgium and the need for constitutional engineering to address this is one prima facie example of such a mid-term rule change

A more prosaic and more common situation in which a qualified majority decision rule can effectively be imposed unexpectedly arises from the

13A very strong party in Laver and Shepsles terms is a party with an ideal point that has an empty winset That is there is no portfolio allocation (ie government) preferred by a parliamentary majority to the one in which the party in question receives all key portfolios

14Since this party is very strong the opposition parties by definition prefer it to the status quo


emergence in the legislature of an anti-system party or of one or more inde- pendents15 An anti-system party that votes against everything as part of a wider strategy to destabilize legislative politics as a whole or independents whose preferences are not well-known and who vote apparently at random effectively add votes to the anti-government side of every division regard- less of its content This leaves the remaining parties needing a majority vote in the legislature when all legislative votes are not available to them Thus if there are 10 maverick voters in a 200 seat legislature the decision rule requires 101 out of 190available voters not out of 200 and a qualified majority decision rule is effectively in operation If the maverick votes come into being as a result of some shock to the system during the lifetime of a particular government then this is a de facto decision rule shock and it may under- mine government stability16

To om knowledge nothing has been written on government survival under qualified majority decision rules and strategic interaction in such circumstances is clearly complex and difficult to characterize We certainly do not have the space to go into such matters here-the important point to note is that a decision rule shock resulting from the unexpected emergence or dis- appearance of mavericks can destabilize an existing equilibrium

Classes of Critical Event Putting all of this together we see that having a model of government

equilibrium allows us to identify classes of critical event that might destabilize that equilibrium A model has variables that contribute towards iden- tifying an equilibrium A particular equilibrium outcome is conditioned on certain values of these variables these values being parameters of the equilibrium concerned Each variable is associated with a class of relevant critical event an event capable of perturbing the values of the variable enough to destroy the equilibrium Indeed in the world as conceived by any model all relevant critical events rnust derive their relevance by perturbing the values of some model variable since if all such values remain unchanged the equilibrium analysis derived from the model must remain unchanged also and the status quo remain intact

Thus having a model of government equilibrium is an essential step in any systematic analysis of the impact of events on government survival and it is in this sense that we observed earlier that purely inductive approaches are incomplete The Lupia-Strom account of government survival derives

15Although for this to happen mid-term the anti-system party would need to be a split from an existing pro-system party

160ne of the anonymous referees observed that exogenous decision-rule shocks are especially plausible when applied to parliaments operating under something short of full sovereignty such as subnational assemblies or increasingly national parliaments within the EU


from a model of government equilibrium driven by expectations about future election results This leads to a concentration on public opinion shocks as a class of critical event The Laver-Shepsle account is based on a range of different variables as we have seen each of which defines a different class of critical event17 In what follows we explore the impact of different types of critical event on the stability of some real-world equilibrium governments Before this however we set out the simulation technology that allows us to do so

Simulating Critical Events In principle it should be possible to use the analytic methods of com-

parative statics to evaluate the impact of perturbing key model parameters on a particular government equilibrium This is in effect what Lupia and Strom do for the three-party case Laver and Shepsle (1993) also explore government equilibrium in the three-party two-ditnensional case analytically In practice when using the portfolio allocation model to consider more complex cases however the impact of interactions between model parameters on equilibrium forecasts is not only complex but is fundamentally characterized by sudden discontinuities in the face of continuous changes in individual variables Strategic thresholds for example the indifference curves of pivotal actors are suddenly crossed generating new voting majorities when party ideals or party-specific salience weights are continu- ously varied New sets of winning coalitions are suddenly generated from smooth changes in party weights and so on Analytical expressions about the relationship between model parameters and government equilibrium can be written down but they are large and ugly and lack any intuitive connection to the real world l s

Since analytical techniques are impractical we use simulations to explore the ability of particular equilibrium cabinets to survive perturbations in model parameters We simulate a stream of political shocks by adding a series of random disturbance terms to key party system parameters and observing the proportion of these that destabilize a given equilibrium Compar- ing two equilibrium cabinets the cabinet that is destabilized by the higher proportion of random shocks is taken to be the less stable The proportion of a stream of random shocks of fixed amplitude that a given equilibrium cabinet survives can be taken as an estimate of its relative stability vis ZI vis com- parable equilibrium cabinets exposed to the same shock stream

171n fact the Laver-Shepsele model allows for several different forms of equilibrium only the most prominent of which we have described here

I8Some large ugly and nonintuitive expressions derived from the portfolio allocation model are on display in Laver and Shepsle (1993)


In practice if we want to estimate for example the impact of agenda shocks on a given equilibrium government we generate a set of shocked cases each representing a perturbation in the base case under investigation after an event alters party-specific dimension weights In the results that we report in this paper we used 1000 shocked cases for each simulation In the case of an agenda shock each shocked case is derived by adding a random disturbance term to the base case weight attached by each party to each dimension This disturbance term is randomly drawn from a normal distribution with a mean of zero and a standard deviation of s where the magnitude of s determines the amplitude of the shock stream to which we expose the base case A larger s is likely to expose dimension weights to larger perturbations The standard deviation s of the shock term is thus a parameter that characterizes the variation in the size of the shocks being modeled-in effect the amplitude of the shock stream to which the base case is subjected19 By increasing s a more vigorous and destructive shock stream can be simulated

The stability of the equilibria generated by two different base cases can be compared using simulated shock streams such as these Each base case is perturbed a fixed number of times by random shocks drawn from a stream of fixed amplitude Some of these shocks will create a shocked case in which the models predicted equilibrium cabinet is identical to that in the base case Some will create a shocked case in which the anticipated outcome is not the same as in the base case The higher the proportion of shocked cases in which the newly created equilibrium is identical to the base case equilibrium the more stable the base case is taken to be An identical technique can be used to explore the effects of policy or public opinion shocks while the effects of decision-rule shocks can be explored using more conventional analytical means20

Our theoretical approach of modeling cabinet stability in terms of robustness to perturbations in party system parameters as well as our basic simulation technology is appropriate for any well-specified model of cabinet equilibrium Provided a model of cabinet equilibrium can be well-enough

I9It is worth noting that holding s constant over a given set of simulated shocked cases amounts to assuming in the language of event history analysis that the cabinet under investigation has a constant hazard rate It is in principle possible to simulate variable (most often thought of as rising) hazard rates by varying s in some well-specified way during the simulation But we do not attempt this in the present paper See Warwick (1994) for a discussion of constant and variable hazard rates

201n fact this proves to be a conservative measure of stability for we count every instance in which a parameter shock no longer supports the prior equilibrium as actually disequilibrating it But as Sven Feldmann has pointed out to us not all destabilizing events are disequilibrating events Forward-looking institutional actors may not desert the prior equilibrium deciding to jump ship only if they are certain they will be better off when the process their desertion sets into motion settles down into a new equilibrium


specified to be programmed a particular party system configuration under investigation can be taken as comprising a base case to which random perturbations of key parameters can systematically be applied The equilibrium can be recalculated in the light of each perturbation allowing the investiga- tor to estimate the proportion of such perturbations to which the base case equilibrium is robust using this to generate an estimate of relative stability There is nothing about this methodology that is specific to the portfolio allocation approach

The Relative Stability of Real Cabinets In this section we use the Laver-Shepsle portfolio allocation model of

government equilibrium and the simulation technology we have just described to explore the relative ability of two real-world governments to survive different types of critical event The two cases we consider in some detail are first the Christian Democrat (CDU)-Free Democrat (FDP) coalition that formed in Germany in 1987 and second the Fianna FBil (FF)-Labour (Lab) coalition that formed in Ireland in 1992

Our choice of these cases is far from accidental The most persuasive two-dimensional representation of each case generates a very clear cut equilibrium government according to the portfolio allocation model In each case taking the key portfolios as Finance and Foreign Affairs the cabinet that actually formed was one allocating each key portfolio to the party con- trolling the median legislator on the main policy dimension over which the portfolio had jurisdiction This dimension-by-dimension median cabinet gave the Finance portfolio to the CDU and Foreign Affairs to the FDP in Germany In Ireland it gave Finance to FF and Foreign Affairs to Labour Crucially in each case no alternative portfolio allocation was preferred by a legislative majority to the portfolio allocation that occurred the latter alloca- tions winset was empty In each case therefore the government that formed was in equilibrium No actor with an incentive to bring down the incumbent government also had the ability to do so while none with the ability to do so also had the incentive

It may on the face of things seem to be cheating to concentrate only upon equilibrium governments when we analyze government survival A moments thought however reveals that this is in fact the only thing that we can sensibly do given our argument that we must analyze government survival by using an explicit model to explore the events that knock an equilibrium government out of equilibrium In a very real sense we have nothing at all to say about the stability of out-of-equilibrium governments Since our model cannot account for why they formed in the first place it cannot possi- bly account for why they fall This is not a problem unique to our approach but applies to any approach that sees the fall of a government as the collapse


of an equilibrium (eg Austen-Smith and Banks 1988 1990 Baron 1991 Schofield 1993) If the equilibrium in place is not anticipated by a model then its collapse must depend upon factors outside the models scope

We operationalize our exploration of the two governments concerned using the same dataset as Laver and Shepsle (1996) to identify equilibrium governments These data involve specifications of key policy dimensions and cabinet portfolios of actual party policy positions and party-specific dimension weights and of legislative seat distributions and the actual allocation of key portfolios While most of these operationalizations could of course be discussed at great length it is not our purpose in the current paper to do so The basic data for both cases are given in Table 221

Using these data we first confirmed that the status quo portfolio allocation in the Irish and German cases was indeed in equilibrium using the com- puter program developed by Laver and Shepsle for applying the portfolio allocation The Finance-Foreign Affairs portfolio allocation to FF-Lab in Ireland and CDUICSU-FDP in Germany had an empty winset in each instance We then used the same program to perform a wide range of simulations that explored the sensitivity of each equilibrium government to perturbations of party-specific dimension weights party policy positions and party seat distributions These simulations thus explored the ability of the Irish and German governments under investigation to survive agenda shocks policy shocks and public opinion shocks respectively

Agenda Shocks We first explored the susceptibility of the two equilibrium governments

to agenda shocks We did this by exposing each base case to a series of shock streams each stream of increasing amplitude and observing the proportion of shocked cases in each stream for which the base case equilibrium cabinet remained in equilibrium Each shocked case was generated by taking each party-specific dimension weight in the base case and adding a random disturbance term as described earlier The first shock stream of 1000 cases had a relatively low amplitude Each successive shock stream applied to a particular equilibrium government had a greater amplitude causing greater perturbations to the party-specific dimension weights in the base

2In Laver and Shepsle (1996) we developed the German and Irish cases both as a two-dimensional and a three-dimensional portfolio allocation situation Here we present only the former to keep exposition simple and the running of the simulations manageable

The program itself (called WINSET) program manuals and sample data files can be down- loaded over the Internet for personal academic use by connecting to FTPTCDIE logging on as user anonymous and supplying a complete e-mail address as a password The latest release ver- sions of all files are located in the directory PUBPOLITICS All analyses in this paper can be rep- licated using this program and the data in Table 2


Table 2 Party Positions Legislative Seats and Dimension Weightings Germany 1987

FOREIGN FINANCE AFFAIRS

Increase taxes ( 1 ) Pro ( I ) vs vs cut services (20) anti (20) USSR

Seats Position Weight Position Weight

Christian Democratic Union1 Christian Social Union (CDUICSU) 223 135 139 98 124

Social Democratic Party (SPD) 186 65 125 46 132

Free Democrats (FDP) 46 157 152 66 138

Greens (G) 42 52 98 40 98

Total Majority threshold

Source Party positions taken from Laver and Hunt (1992 197)

Ireland 1992


Pro (1) vs Increase taxes (1 ) anti (20) British

vs cut services 120) aresence in NI


Fianna FBil (FF) 68 131 126 158 124

Fine Gael (FG) 45 150 155 100 123

Labour (Lab) 33 69 130 124 105

Progressive Democrats (PD) 10 176 164 106 107

Democratic Left (DL) 4 45 125 76 153

Others 5

Total Chair Maioritv threshold

Source Party positions taken from Laver (1994 163)

case In effect this amplitude-the standard deviation s-was a knob that we could turn to increase the violence of the shock stream to which we exposed each government


Party-specific dimension weights in the dataset were denominated on a scale from one to 20 The mildest shock stream we report was generated by adding to these weights random disturbance terms drawn from a normal distribution with a mean of zero and a standard deviation of 100 and holding all other parameters constant Since the standard deviation of the shock terms in this most tranquil shock stream was 5 of the maximum party-specific dimension weight almost all shocks would leave dimension weights within 10 of their original base case value After a thousand runs (sets of random draws) at this setting for s we then produced another stream of 1000 using a standard deviation of 150 we then generated a shock stream using an s of 200 and so on The effect was rather like putting a model of the government under investigation into a wind tunnel then exposing the modeled government to ever more violent winds so that we could observe when and how it was ultimately blown apart

In order to estimate the maximum possible susceptibility to agenda shocks of the equilibrium government under investigation given a fixed configuration of party policy positions and decisive structure we also generated a shock stream in which party specific dimension weights were simply random numbers drawn from a uniform distribution on the [I 201 interval On these most extreme assumptions the stream of agenda shocks is so violent that party specific dimension weights in each shocked case cannot be predicted at all from those in the base case

The results of exposing the governments under investigation to shock streams with amplitudes from 1 to 35 are given in Table 3 each cell of which reports the results of a 1000 case ~ i m u l a t i o n ~ ~ This also shows the results of the maximal shock stream with totally random dimension weights The results in Table 3 show for a given amplitude of shock stream s the proportion of cases for which the base case equilibrium was no longer an equilibrium in the shocked case This is reported as the governmental death rate per shock in the table Note in this instance that a shock to party- specific dimension weights cannot change the identity of the dimension by dimension median cabinet which must remain the same as the base case in all shocked cases since party positions are not being altered What changes with the shocks is the relative salience of each dimension to a party This in turn determines whether or not some alternative cabinet is preferred by a majority to the base case dimension-by-dimension median cabinet

To take a specific example from Table 3 if exposed to an agenda shock stream of amplitude 200 then the German government in 1987 had a death rate per shock of 0057 In other words 57 out of 1000 agenda shocks in a

23Shock streams of amplitude greater than 35 caused problems in simulations of agenda shocks using this dataset since given the base case configurations of party specific dimension weights they sometimes generated negative dimension weights

Michael Laver and Kenneth A Shepsle

Table 3 Simulated Agenda Shocks Germany 1987 Ireland 1992

Dimwt(p d) = BaseDimwt(p d) + Normal (0 s)

Shock streanz Governn~ental anzplitude s death rateshock

Gernzany Ireland

random dimension weights

stream of this amplitude destabilized the status quo This gives an expected duration of 1000157 or 175 of the shocks in this stream24 In contrast the Irish government forming in 1992 had an estimated death rate per shock of 0004 in a shock stream of similar amplitude giving an expected duration of 250 of the shocks in this stream

If we attempt to relate these simulations to the absolute real-time survival rates of the governments under investigation of course we are ham- strung by having no idea whatsoever of the most appropriate value of s to model agenda shock streams in a particular real-world case The simulations do nonetheless give us some very useful insights In the examples explored in Table 3 for example we do observe that the German government has a higher death rate than the Irish government for every value of s investigated (And given the figures in the table it seems reasonable to extrapolate and interpolate results for other values of s to infer that this finding holds for all values of s) These results do therefore indicate strongly that other things being equal the German government in 1987 was distinctly more susceptible to agenda shocks than was its Irish counterpart in 199225

241f we know the mean real-time frequency of agenda shocks in a stream of amplitude s = 2 then this would allow us to estimate an expected duration in real time But of course we do not

To reiterate however if such shocks were decidedly less frequent in real-time Germany than in real-time Ireland it is perfectly legitimate to expect a German government lasting longer than its Irish counterpart


Table 4 Simulated Policy Shocks Germany 1987 Ireland 1992

Position(p d) = BasePosition(p d) + Normal (0 s)

Shock stream Governmental an~plitudes death ratehhock

Germany Ireland

random party positions

Policy Shocks The susceptibility of each government to policy shocks is explored in a

closely analogous way in Table 4 The results in this table were estimated by simulating streams of shocked cases each of which was generated by adding random disturbance terms to the party policy positions reported in Table 2 holding all other parameters constant Party policy positions were also expressed in the data on a scale running from one to 20 for each dimension The random disturbance term added to each policy position on each dimension was independently drawn from a normal distribution with a mean of zero and a standard deviation of s The most tranquil shock streams had a standard deviation of 05 so that most shocked policy positions were once more within 10 of their original value Ever more violent shock streams were generated up to a maximum amplitude of 50 Once more the effects of a maximal shock stream were calculated as a benchmark given base case dimension weights and decisive structure using a shock stream in which party policy positions were drawn completely at random from a uniform distribution on the [ I 201 interval

The results of applying streams of policy shocks to the two cases under investigation is shown in Table 4 In striking contrast to the impact of agenda shocks policy shock streams of equivalent amplitude had a much


more destabilizing effect This almost certainly arises from the vital role of the dimension-by-dimension median cabinet in determining the equilibrium in this model and the fact that perturbations of party policy positions can obviously change this in a way that perturbation of party-specific dimension weights cannot Table 4 also shows that equivalent streams of policy shocks had a more destabilizing effect on the 1992 Irish government than on the 1987 German government The Irish government was in particular much more sensitive to relatively small perturbations in party policy positions with a death rate per shock of 0257 in the shock stream of amplitude 05 as opposed to a death rate in equivalent circumstances of 0001 for the German government The Irish government is more susceptible than the German government to policy shock streams of every amplitude investigated or rea- sonably interpolated

This suggests very strongly that the configuration of Irish policy positions puts the Irish case much closer to one or more strategic thresholds than was the German case the latter thus requiring more vigorous policy shocks to destabilize it The net result was that the Irish government was much more vulnerable to policy shocks

Public Opinion Shocks The susceptibility of each government to public opinion shocks is ex-

plored in Table 5 Streams of public opinion shocks were generated by perturbing party seat totals to simulate party expectations about the results of an immediate election Each party seat total was perturbed by adding a random disturbance term drawn from a normal distribution with a mean of zero and a standard deviation of (s) x (S)20 where S was the number of seats won by party p in the base case and s was once more a parameter describing the violence of the shock stream Thus when s was set to one the standard deviation of shocks was 5 of the original party seat total making it broadly analogous to values of s in other types of shock stream In this relatively tranquil shock stream almost all shocks would change seat totals no more than 10 from their original value The impact of ever more violent shock streams was also modeled to a maximum of s = 5 In addition as a benchmark of the impact of maximal public opinion shocks a series of shocked cases was generated in which party seat totals were randomly drawn from a uniform distribution on the [O 1001 interval In all cases the number of seats controlled by each party in each shocked case was totaled and the majority threshold recalculated accordingly

The overall results in Table 5 show the vulnerability of the two equilibrium cabinets under investigation to public opinion shocks that give some party an incentive to force an early election The results of these simulations show the Irish government in 1992 to have been much more susceptible to


Table 5 Simulated Public Opinion Shocks Germany 1987 Ireland 1992

Seats(p) = BaseSeats(p) + Normal (0 s BaseSeats(p)20)

Shock stream Governmental amplitude s death rateshock

Germany Ireland CDU very FF very

overall strong overall strong

random 0046 0011 party (0047 FDP) (0066Lab) seats

relatively modest levels of this type of public opinion shock than was the German government in 1987 In a shock stream that almost never perturbs party seat totals by more than 10 of their original value (s = I) the Ger- man government has a death rate per shock of 0005 while the Irish government had a death rate of 0264

We should recall however that the portfolio allocation model identifies as destabilizing only those public opinion shocks that make some member of a coalition cabinet very strong (see Laver and Shepsle 1996 chap 4) when before it was not Public opinion shocks improving the strategic position of the opposition however dramatically should have no effect on the stability of the government neither should shocks improving the electoral prospects of government members somewhat but not enough to secure for them a more favorable equilibrium government Thus Table 5 also shows the proportion of shocks in each shock stream that made the PMs party very strong While other public opinion shocks might destabilize governments if we ignore the PMs control over the calling of elections only these more re- stricted types of shock can give the PM an incentive to force an election and be in this way de~tabi l iz ing ~~

26As it happens never in the shock streams investigated was the non-PM government party made very strong


These figures show that the asymmetry between the PMS party and others in regard to calling an election makes a very substantial difference to the impact of public opinion shocks on government survival In both countries the government was much less vulnerable to public opinion shocks once the PMs control over calling an election was taken into account Many of the simulated public opinion shocks helped opposition parties which have no control over calling an election Other public opinion shocks may have fa- vored the government parties but not enough to improve their position in the government expected to result from an immediate election We once more have striking evidence that institutional details such as this can make a big big difference

Where Are We Now The essential point of this paper has been to develop a theoretical ac-

count of government survival within the critical events tradition Our approach develops the ideas of the original events theorists who had no model of government equilibrium and thus took every government as an equilibrium in its own terms Instead however we take a well-specified model of government equilibrium and explore ways in which critical events affect particular equilibrium governments Our approach complements the one recently put forward by Lupia and Strom who use a model of government equilibrium to characterize government survival analytically with analytical complexities restricting the substance of their account to only one type of critical event in (untypical) three-party systems We use simulations to side- step analytical complexities and apply these to a model that identifies the impact of different classes of critical event in party systems of any size

Our simulation technology allows us to explore exhaustively aspects of the stability of individual base cases and in this paper we explored the cases of Germany in 1987 and Ireland in 1992 For the particular cases under investigation we can use simulations based on the portfolio allocation model to look at the susceptibility of different governments to different types of shock As a result of this we see that cases which might on the face of things look rather similar can in fact be unstable in different ways with some types of critical event being more dangerous for some governments and other types of critical event being more dangerous for others The approach thus allows us to use the model to make what is really quite a systematic and fruitful exploration of individual cases As such it is an example of something that is relatively rare in political science-the use of a rigorous general model in specific case studies27

2 7 B ~ tnothing comes free o f course The very richness that commends the approach to case studies that characterizes each case in terms o f a range o f parameters and that thereby identifies different types o f critical event which may have a bearing on government stability makes each case


The question that remains concerns whether it is actually useful or even possible to talk about government survival in general Two five-party systems with identical decisive structures for example can have very different stability characteristics according to our approach arising from different configurations of party ideal points One configuration of ideal points may leave some crucial indifference curve very close to a strategic threshold- the other may not Two five-party systems with identical configurations of party ideals and dimension weights may also have identical decisive structures but one decisive structure may derive from a set of party weights for which small changes in seat totals change the decisive structure while the other requires much larger changes in seat total to change the decisive structure Again the two superficially identical governments may have very different stability characteristics as a consequence

Given all of this and despite the fact that we can use a model to analyze individual cases in a rigorous manner general statements about government stability should only be made with caution This implies that previous general statements about government stability may perhaps have been rather too sanguine and that we should be grateful for the solid ground that the model places under our feet when we attempt the systematic analysis of individual cases

Manuscript submitted 9 October 1996 Final manuscript received 18 February 1997

REFERENCES

Austen-Smith David and Jeffrey Banks 1988 Elections Coalitions and Legislative Outcomes American Political Science Review 82 405-22

Austen-Smith David and Jeffrey Banks 1990 Stable Governments and the Allocation of Policy Portfolios American Political Science Review 84891-907

Baron David 1991 A Spatial Bargaining Theory of Government Formation in Parliamentary Sys- tems American Political Science Review 85 137-65

Bates Robert Avner Greif Margaret Levi Jean-Laurent Rosenthal and Barry Weingast 1997 Analytical Narratives Harvard University Typescript

Browne Eric C John P Frendreis and Dennis Gleiber 1984 An Events Approach to the Prob- lem of Cabinet Stability Comparative Political Studies 17 167-97

Browne Eric C John P Frendreis and Dennis Gleiber 1986 The Process of Cabinet Dissolution An Exponential Model of Duration and Stability in Western Democracies American Journal ofPolitica1 Science 30628-50

Browne Eric C John P Frendreis and Dennis Gleiber 1988 Contending Models of Cabinet Sta- bility A Rejoinder American Political Science Review 8293041

look very different from every other For a related consideration of juxtaposing case studies and analytical methods see Bates et al (1997)


Gallaher Michael Michael Laver and Peter Mair 1995 Representative Government in Modern Europe New York McGraw-Hill

Grofman Bernard and Peter van Koozendaal 1994 Toward a Theoretical Explanation of Prema- ture Cabinet Termination with Application to Post-war Cabinets in the Netherlands European Journal of Political Research 26 155-70

Huber John 1995 The Impact of Confidence Votes on Legislative Politics in Parliamentary Sys- tems Presented to the Workshop on Party Discipline and the Organization of Parliaments ECPR Joint Sessions Bordeaux

Huber John 1996 The Vote of Confidence in Parliamentary Democracies American Political Science Review 90269-83

King Gary James Alt Nancy Burns and Michael Laver 1990 A Unified Model of Cabinet Dis- solution in Parliamentary Democracies American Journal of Political Science 34846-71

Laver Michael 1994 Party Policy and Cabinet Portfolios in Ireland 1992 Results from an Expert Survey Irish Political Studies 9 157-64

Laver Michael and W Ben Hunt 1992 Policy and Party Competition New York Routledge Laver Michael and Norman Schofield 1990 Multipart) Government the Politics of Coalition in

Europe Oxford Oxford University Press Laver Michael and Kenneth A Shepsle 1990 Coalitions and Cabinet Government American

Political Science Review 84873-91 Laver Michael and Kenneth A Shepsle 1993 A Theory of Minority Government in Parliamen-

tary Democracy In Games in Hierarchies and Networks ed Fritz W Scharpf Boulder CO Westview Press

Laver Michael and Kenneth A Shepsle 1996 Making and Breaking Governments New York Cambridge University Press

Lupia Arthur and Kaare Strom 1995 Coalition Termination and the Strategic Timing of Legisla- tive Elections American Political Science Review 89648-65

Sanders David and Valentine Herman 1977 The Stability and Survival of Governments in West- ern Democracies Acta Politica 12346-77

Schofield Norman 1993 Political Competition and Multiparty Coalition Government European Journal ofPolitica1 Research 23l-33

Shepsle Kenneth A 1991 Models of Multiparty Electoral Competition Chur Switzerland Harwood Academic Publishers

Strom Kaare 1985 Party Goals and Government Performance in Parliamentary Democracies American Political Science Review 79738-54

Taylor Michael and Valentine Herman 1971 Party Systems and Government Stability American Political Science Review 6528-37

Warwick Paul 1979 The Durability of Coalition Governments in Parliamentary Democracies Comparative Political Studies 11465-98

Warwick Paul 1994 Government Survival in Parliamentary Democracies New York Cambridge University Press

Events Equilibria and Government Survival Michael Laver Trinity College Dublin Kenneth A Shepsle Harvard University

Theory A game-theoretic model of government formation yields an equilibrium government the robustness of which may be explored by subjecting it to exogenous shocks This permits an examination of government durability and survival in a cruel political world Hypotheses The vulnerability of a government to exogenous shocks depends upon the nature of the shock A government may be quite resistant to some classes of shock while it is highly vulnerable to others Methods Game-theoretic analysis yields equilibrium results A simulation technology is crafted which allows us to subject this equilibrium to perturbations of its underlying parameters (much in the spirit of wind-tunnel experiments in engineering) Results The technology does indeed allow the systematic examination of well-defined cases We find for the case of two European governments in the 1980s and 1990s that they differ considerably in their vulnerability to exogenous shocks

Introduction In order to understand the workings of parliamentary government one

must determine what it takes for a government to survive in a cruel political world In order to do this we must understand the circumstances that led to a particular government taking office in the first place and the circumstances in which this government would be replaced by some alternative This con- centrates our attention on how radically circumstances must change before a government falls and is replaced If a government can survive dramatic changes in its political environment while still managing to hold on to the reins of power we think of it as relatively stable If a government cannot survive even quite small changes to the environment in which it originally took office we think of it as being relatively unstable

This paper is concerned with government survival in parliamentary democracies exploring factors that might destabilize equilibrium governments This is not just an abstract academic problem In practical political terms the survival potential of any real-world government is of obvious interest to the wide range of actors who must deal with it These include among many others opposition parties citizens interest groups revolution-

This paper was originally prepared for the Annual Meeting of the American Political Science As- sociation San Francisco 1996 We are grateful for the comments there from Sven Feldmann and Barry Weingast For programming assistance we thank Paul Doyle We also gratefully acknowledge the comments of three anonymous referees

American Journal of Political Science Vol 42 No 1 January 1998 Pp 28-54 O 1998 by the Board of Regents of the University of Wisconsin System






































































































































Greens (G) 42 52 98 40 98



Ireland 1992





Fianna FBil (FF) 68 131 126 158 124

Fine Gael (FG) 45 150 155 100 123

Labour (Lab) 33 69 130 124 105



Others 5














Gernzany Ireland










Germany Ireland































REFERENCES


































































































































































Greens (G) 42 52 98 40 98



Ireland 1992





Fianna FBil (FF) 68 131 126 158 124

Fine Gael (FG) 45 150 155 100 123

Labour (Lab) 33 69 130 124 105



Others 5














Gernzany Ireland










Germany Ireland































REFERENCES


























































































































































Greens (G) 42 52 98 40 98



Ireland 1992





Fianna FBil (FF) 68 131 126 158 124

Fine Gael (FG) 45 150 155 100 123

Labour (Lab) 33 69 130 124 105



Others 5














Gernzany Ireland










Germany Ireland































REFERENCES




















































































































































Greens (G) 42 52 98 40 98



Ireland 1992





Fianna FBil (FF) 68 131 126 158 124

Fine Gael (FG) 45 150 155 100 123

Labour (Lab) 33 69 130 124 105



Others 5














Gernzany Ireland










Germany Ireland































REFERENCES













































































































































Greens (G) 42 52 98 40 98



Ireland 1992





Fianna FBil (FF) 68 131 126 158 124

Fine Gael (FG) 45 150 155 100 123

Labour (Lab) 33 69 130 124 105



Others 5














Gernzany Ireland










Germany Ireland































REFERENCES







































































































































Greens (G) 42 52 98 40 98



Ireland 1992





Fianna FBil (FF) 68 131 126 158 124

Fine Gael (FG) 45 150 155 100 123

Labour (Lab) 33 69 130 124 105



Others 5














Gernzany Ireland










Germany Ireland































REFERENCES
































































































































Greens (G) 42 52 98 40 98



Ireland 1992





Fianna FBil (FF) 68 131 126 158 124

Fine Gael (FG) 45 150 155 100 123

Labour (Lab) 33 69 130 124 105



Others 5














Gernzany Ireland










Germany Ireland































REFERENCES


























































































































Greens (G) 42 52 98 40 98



Ireland 1992





Fianna FBil (FF) 68 131 126 158 124

Fine Gael (FG) 45 150 155 100 123

Labour (Lab) 33 69 130 124 105



Others 5














Gernzany Ireland










Germany Ireland































REFERENCES


















































































































Greens (G) 42 52 98 40 98



Ireland 1992





Fianna FBil (FF) 68 131 126 158 124

Fine Gael (FG) 45 150 155 100 123

Labour (Lab) 33 69 130 124 105



Others 5














Gernzany Ireland










Germany Ireland































REFERENCES






































































































Greens (G) 42 52 98 40 98



Ireland 1992





Fianna FBil (FF) 68 131 126 158 124

Fine Gael (FG) 45 150 155 100 123

Labour (Lab) 33 69 130 124 105



Others 5














Gernzany Ireland










Germany Ireland































REFERENCES





























































































Greens (G) 42 52 98 40 98



Ireland 1992





Fianna FBil (FF) 68 131 126 158 124

Fine Gael (FG) 45 150 155 100 123

Labour (Lab) 33 69 130 124 105



Others 5














Gernzany Ireland










Germany Ireland































REFERENCES





















































































Greens (G) 42 52 98 40 98



Ireland 1992





Fianna FBil (FF) 68 131 126 158 124

Fine Gael (FG) 45 150 155 100 123

Labour (Lab) 33 69 130 124 105



Others 5














Gernzany Ireland










Germany Ireland































REFERENCES
















































































Greens (G) 42 52 98 40 98



Ireland 1992





Fianna FBil (FF) 68 131 126 158 124

Fine Gael (FG) 45 150 155 100 123

Labour (Lab) 33 69 130 124 105



Others 5














Gernzany Ireland










Germany Ireland































REFERENCES








































































Greens (G) 42 52 98 40 98



Ireland 1992





Fianna FBil (FF) 68 131 126 158 124

Fine Gael (FG) 45 150 155 100 123

Labour (Lab) 33 69 130 124 105



Others 5














Gernzany Ireland










Germany Ireland































REFERENCES
































































Greens (G) 42 52 98 40 98



Ireland 1992





Fianna FBil (FF) 68 131 126 158 124

Fine Gael (FG) 45 150 155 100 123

Labour (Lab) 33 69 130 124 105



Others 5














Gernzany Ireland










Germany Ireland































REFERENCES

























































Greens (G) 42 52 98 40 98



Ireland 1992





Fianna FBil (FF) 68 131 126 158 124

Fine Gael (FG) 45 150 155 100 123

Labour (Lab) 33 69 130 124 105



Others 5














Gernzany Ireland










Germany Ireland































REFERENCES



















































Greens (G) 42 52 98 40 98



Ireland 1992





Fianna FBil (FF) 68 131 126 158 124

Fine Gael (FG) 45 150 155 100 123

Labour (Lab) 33 69 130 124 105



Others 5














Gernzany Ireland










Germany Ireland































REFERENCES













































Greens (G) 42 52 98 40 98



Ireland 1992





Fianna FBil (FF) 68 131 126 158 124

Fine Gael (FG) 45 150 155 100 123

Labour (Lab) 33 69 130 124 105



Others 5














Gernzany Ireland










Germany Ireland































REFERENCES





































Greens (G) 42 52 98 40 98



Ireland 1992





Fianna FBil (FF) 68 131 126 158 124

Fine Gael (FG) 45 150 155 100 123

Labour (Lab) 33 69 130 124 105



Others 5














Gernzany Ireland










Germany Ireland































REFERENCES







































Gernzany Ireland










Germany Ireland































REFERENCES

































Gernzany Ireland










Germany Ireland































REFERENCES

































Germany Ireland































REFERENCES























































REFERENCES

















































REFERENCES







































REFERENCES

































REFERENCES

















































Technology

Shepsle Laver Events Equilibria