Traditional Epidemiology, ModernEpidemiology, and Public Health
Neil Pearce, PhD
IntroductionIn this article I consider some of the
key features ofwhat has become known asmodern epidemiology, and I contrastthese with more traditional approaches. Ido not intend to present a detailedhistorical review,1-3 nor to present acomprehensive review of current ap-proaches. Rather, I will focus on some ofthe key changes in epidemiology over thepast few decades, and I will consider theconcepts of causality involved and theirideological and practical consequences. Iwill argue that the rise ofmodem epidemi-ology has been a mixed blessing and thatthe new paradigm has major shortcom-ings, both in public health and in scientificterms.4 The recent changes in epidemio-logic methodology have not been neutral,but rather (in combination with otherinfluences) they have changed-and havereflected changes in-the way in whichepidemiologists think about health anddisease.5 The key issue has been the shiftin the level of analysis from the popula-tion to the individual (S. Wing, Conceptsin modem epidemiology: population, risk,dose-response, and confounding, unpub-lished manuscript). This is typified by thecurrent lack of interest in populationfactors as causes of disease, the lack ofinterest in the history of epidemiology,and the lack of integration with otherpublic health activities. I will give particu-lar emphasis to the current neglect ofsocial, economic, cultural, historical, politi-cal, and other population factors, and Iwill refer to these using the general termof "socioeconomic factors."
Of course, traditional epidemiologywas not a monolith. A wide variety ofapproaches were used, and there is adanger of setting up caricatures of idealtypes. It should also be emphasized thattraditional epidemiology gave rise to
modern epidemiology; therefore, theyhave many features in common. Neverthe-less, there are some important differencesbetween the traditional and the modernapproaches, particularly the loss of thepopulation perspective in recent decades.I therefore will discuss some of thereasons the population perspective hasbeen lost and the implications of thisparadigm shift. Then, I will discuss someof the key issues in developing new formsof epidemiology that restore the popula-tion perspective while making use ofrecent methodological advances. (I amtempted to use the term "postmodernepidemiology" to provide a contrast withmodern epidemiology and because somepostmodernist concepts are relevant tomy arguments; however, the use of thisterm could imply an uncritical advocacy ofpostmodernism, which has its own episte-mological and practical shortcomings.)
Traditional and ModernEpidemiology
In the first week of their training,most epidemiologists usually leam a littleabout the history of public health. Inanglophone countries they learn aboutthe work of Chadwick, Engels, Snow, andothers, who exposed the appalling socialconditions during the industrial revolu-tion, and the work of Farr and others, whorevealed major socioeconomic differencesin disease in the 19th century. At thattime, epidemiology was a branch of public
The author is with the Wellington School ofMedicine, Wellington, New Zealand.
Requests for reprints should be sent toNeil Pearce, PhD, Wellington School of Medi-cine, PO Box 7343, Wellington, New Zealand.
This article was accepted June 22, 1995.Editor's Note. See related editorial by
Winkelstein (p 621) in this issue.
May 1996, Vol. 86, No.5
Epidemiology and Public Health
health and focused on the causes andprevention of disease in populations, incontrast to the clinical sciences, whichwere branches of medicine and focusedon disease pathology and treatment ofindividuals (S. Wing, Concepts in modemepidemiology: population, risk, dose-response, and confounding, unpublishedmanuscript). Thus, the emphasis was onthe prevention of disease and the healthneeds of the population as a whole. Thedramatic decline in infectious diseasesthat has occurred since the mid-19thcentury has been attributed to improve-ments in nutrition, sanitation, and generalliving conditions,6 although it has beenargued that specific public health interven-tions regarding factors such as urbancongestion actually played the majorrole.7
There are still major socioeconomicdifferences in health, and the relativedifferences are continuing to increase.8'9Nevertheless, modern epidemiologistsrarely consider socioeconomic factors andthe population perspective, except per-haps to occasionally adjust for social classin analyses of the health effects of tobaccosmoke, diet, and other lifestyle factors inindividuals. For example, studies in mostindustrialized countries have repeatedlyfound strong associations between socialclass and cancer,10 yet social class did notfeature, except for a brief mention as aconfounder, in the most comprehensivereview of the causes of cancer in theUnited States,11 and one leading epidemi-ology text states that "social class ispresumably related causally to few if anydiseases.'2
Traditional epidemiology has be-come unfashionable and is treated some-what disparagingly in modem epidemiol-ogy texts, which have rewritten the historyof epidemiology in their own image. Inparticular, there has been a strong focuson statistical issues and paradigms'3 andan ignorance of the other modes ofthought that were integral to the work of19th-century pioneers such as Snow.'4One is left with the impression that19th-century epidemiologists used ad hocmethods that have now been placed on asounder foundation through recent devel-opments in methods of study design (e.g.,the theory of case-control studies), dataanalysis (e.g., logistic regression), andexposure measurement (e.g., new molecu-lar biology techniques). Epidemiology hasbecome a set of generic methods for themeasurement of disease occurrence, andthere has been a concomittant lack ofdistinctive theory to permit an understand-
TABLE 1-Epidemiological Paradigms
MotivationLevel of study
Context of studyParadigmsEpistemological approachEpistemological strategyLevel of intervention
Historical/culturalDemography/social scienceRealistTop down (structural)Population (upstream)
ing of the population patterns of diseaseoccurrence.15
These methodological developmentshave been paralleled by, and have re-flected, a shift in the level of analysis fromthe population to the individual. Mostmodem epidemiologists still do studies inpopulations, but they do so in order tostudy decontextualized individual risk fac-tors, rather than to study populationfactors in their social and historical con-text. McKinlayl6 argued that what is nowregarded as established epidemiology ischaracterized by biophysiologic reduction-ism, absorption by biomedicine, a lack ofreal theory about disease causation, di-chotomous thinking about disease (every-one is either healthy or sick), a maze ofrisk factors, confusion of observationalassociations with causality, dogmatismabout which study designs are acceptable,and excessive repetition of studies. Heargued that this approach diverts limitedresources, blames the victim, produces alifestyle approach to social policy, decon-textualizes risk behaviors, seldom assessesthe relative contribution of nonmodifiablegenetic factors and modifiable social andbehavioral factors, and produces interven-tions that can be harmful. These trendsare particularly noticeable in the recentrise of molecular epidemiology,'7"18 espe-cially in the renewed emphasis on issuesof individual susceptibility.
The Decline ofPopulationEpidemiology
As Vandenbroucke'9 noted some-what disapprovingly, social explanationsfor illness won't go away and are rediscov-ered with each new generation of epidemi-ologists. However, rather than ask, asVandenbroucke does, why the populationperspective keeps resurfacing, it is per-haps more useful to ask why it keeps
cell/moleculeContext freeClinical trialPositivistBottom up (reductionist)Individual (downstream)
sinking. Some of the reasons for thecurrent lack of interest in the populationperspective may lie in the personal andprofessional situations of epidemiologists.In most countries the main sources offunding are government or voluntaryagencies that have little interest in, orsympathy for, studies of socioeconomicfactors and health. In the last decade,Western countries, particularly anglo-phone countries, have increasingly placedemphasis on individual responsibility, typi-fied by the famous statement by MargaretThatcher20 that "there is no such thing associety, there are only families and indi-viduals." Governments and funding agen-cies have been most supportive of studiesthat focus on individual lifestyle, andepidemiologists, either through choice orthrough necessity, have tended to go"where the money is."
A related issue is that socioeconomicfactors are "not easily modifiable" and are"too political." However, the decision notto study socioeconomic factors is itself apolitical decision to focus on what ispolitically acceptable rather than what ismost important in scientific and publichealth terms.21 Governments have repeat-edly shown that social and economicdifferences are not God-given but aredirectly affected by government policies,albeit in unexpected ways.22-24 For ex-ample, there is some preliminary evidencethat inequitable distribution of the grossnational product can have a more signifi-cant impact on overall national mortalityrates than the actual level of the grossnational product25; in some countries, alarge increase in gross national producthas been accompanied by little benefit interms of health, whereas some relativelypoor countries (e.g. China, Jamaica, CostaRica) have made major improvements in