Types of research design experiments

Types of design - experimentsTypes of design - experiments 11

Types of research design – experimentsTypes of research design – experiments

Chapter 8 in Babbie & Mouton (2001)Chapter 8 in Babbie & Mouton (2001)

Introduction to all research designsIntroduction to all research designs All research designs have specific All research designs have specific

objectives they strive forobjectives they strive for Have different strengths and limitationsHave different strengths and limitations Have validity considerationsHave validity considerations


Validity considerationsValidity considerations

When we say that a knowledge claim (or proposition) When we say that a knowledge claim (or proposition) is valid, we make a JUDGEMENT about the extent to is valid, we make a JUDGEMENT about the extent to which relevant evidence supports that claim to be which relevant evidence supports that claim to be truetrue

Is the interpretation of the evidence given the only Is the interpretation of the evidence given the only possible one, or are there other plausible ones?possible one, or are there other plausible ones?

"Plausible rival hypotheses" = potential alternative "Plausible rival hypotheses" = potential alternative explanations/claimsexplanations/claims e.g. New York City's "zero tolerance" crime fighting strategy e.g. New York City's "zero tolerance" crime fighting strategy

in the 1980s and 1990s - the reverse of the "broken in the 1980s and 1990s - the reverse of the "broken windows" effectwindows" effect


The logic of causal social research in the The logic of causal social research in the controlled experimentcontrolled experiment

Explanatory rather than descriptiveExplanatory rather than descriptive Different from correlational research - one variable is Different from correlational research - one variable is

manipulated (IV) and the effect of that manipulation manipulated (IV) and the effect of that manipulation observed on a second variable (DV)observed on a second variable (DV)

If … then ….If … then ….

E.g.E.g. "Animals respond aggressively to crowding" (causal)"Animals respond aggressively to crowding" (causal) "People with premarital sexual experience have more stable "People with premarital sexual experience have more stable

marriages" (noncausal)marriages" (noncausal)


Three pairs of components:Three pairs of components:

Independent and dependent variablesIndependent and dependent variables Pre-testing and post-testingPre-testing and post-testing Experimental and control groupsExperimental and control groups


ComponentsComponents

VariablesVariables Dependent (DV)Dependent (DV) Independent (IV)Independent (IV)

Pre-testing and post-testingPre-testing and post-testing OO XX O O

Experimental and control groupsExperimental and control groups To off-set the effects of the experiment itself; To off-set the effects of the experiment itself;

to detect effects of the experiment itselfto detect effects of the experiment itself


The generic experimental design:The generic experimental design:

RR OO11 XX OO22

RR OO33 OO44

The IV is an active variable; it is manipulatedThe IV is an active variable; it is manipulated The participants who receive one level of the IV The participants who receive one level of the IV

are equivalent in all ways to those who receive are equivalent in all ways to those who receive other levels of the IVother levels of the IV


SamplingSampling

1. Selecting subjects to participate in the 1. Selecting subjects to participate in the researchresearch Careful sampling to ensure that results can be Careful sampling to ensure that results can be

generalized from sample to populationgeneralized from sample to population The relationship found might only exist in the The relationship found might only exist in the

sample; need to ensure that it exists in the sample; need to ensure that it exists in the populationpopulation

Probability sampling techniquesProbability sampling techniques


SamplingSampling

2. How the sample is divided into two or 2. How the sample is divided into two or more groups is importantmore groups is important to make the groups similar when they start offto make the groups similar when they start off randomization - equal chancerandomization - equal chance matching - similar to quota sampling matching - similar to quota sampling

proceduresprocedures match the groups in terms of the most match the groups in terms of the most

relevant variables; e.g. age, sex, and racerelevant variables; e.g. age, sex, and race


Variations on the standard experimental Variations on the standard experimental designdesign

One-shot case studyOne-shot case study

XX OO

No real comparisonNo real comparison


A famous one-group posttest-only designA famous one-group posttest-only design

Milgram's study on obedienceMilgram's study on obedience Obedience to authorityObedience to authority The willingness of subjects to follow E's orders to give The willingness of subjects to follow E's orders to give

painful electrical shocks to another subjectpainful electrical shocks to another subject A real, important issue here: how could "ordinary" A real, important issue here: how could "ordinary"

citizens, like many Germans during the Nazi period, citizens, like many Germans during the Nazi period, do these incredibly cruel and brutal things?do these incredibly cruel and brutal things?

If a person is under allegiance to a legitimate If a person is under allegiance to a legitimate authority, under what conditions will the person defy authority, under what conditions will the person defy the authority if s/he is asked to carry out actions the authority if s/he is asked to carry out actions clearly incompatible with basic moral standards?clearly incompatible with basic moral standards?


One-group pre-test post-test designOne-group pre-test post-test design

OO11 X X OO22


ExampleExample

We want to find out whether a family literacy We want to find out whether a family literacy programme enhances the cognitive development of programme enhances the cognitive development of preschool-age children.preschool-age children.

Find 20 families with a 4-year old child, enrol the family Find 20 families with a 4-year old child, enrol the family in a high-quality family literacy programmein a high-quality family literacy programme

Administer a pretest to the 20 children - they score a Administer a pretest to the 20 children - they score a mean of say 50 on the cognitive testmean of say 50 on the cognitive test

The family participates in the programme for twelve The family participates in the programme for twelve monthsmonths

Administer a post-test to the 20 children; now they Administer a post-test to the 20 children; now they score 75 on the test - a gain of 25score 75 on the test - a gain of 25


Two claims/conclusions:Two claims/conclusions:

1 The children gained 25 points on 1 The children gained 25 points on average in terms of their cognitive average in terms of their cognitive performanceperformance

2 the family literacy programme caused 2 the family literacy programme caused the gain in scoresthe gain in scores

VALIDITY - rival explanationsVALIDITY - rival explanations


Static-group comparisonStatic-group comparison

XX OO OO


Evaluating research (experiments)Evaluating research (experiments)

We know the structure of researchWe know the structure of research We understand designsWe understand designs We know the requirements of "good" We know the requirements of "good"

researchresearch Then we can evaluate a studyThen we can evaluate a study Is it good? Can we believe its conclusions?Is it good? Can we believe its conclusions? Back to plausible rival hypothesesBack to plausible rival hypotheses


Validity in designsValidity in designs

If the design is not valid, then the If the design is not valid, then the conclusions drawn are not supported; it is conclusions drawn are not supported; it is like not doing research at alllike not doing research at all

Validity of designs come in two parts:Validity of designs come in two parts: Internal validity Internal validity

can the design sustain the conclusions?can the design sustain the conclusions?

External validity External validity can the conclusions be generalized to the can the conclusions be generalized to the

population?population?


Internal validityInternal validity

Each design is only capable of supporting certain Each design is only capable of supporting certain types of conclusionstypes of conclusions e.g. only experiments can support conclusions about causalitye.g. only experiments can support conclusions about causality

Says nothing about if the results can be applied Says nothing about if the results can be applied to the real world (generalization)to the real world (generalization)

Generally, the more controlled the situation, the Generally, the more controlled the situation, the higher the internal validityhigher the internal validity

The conclusions drawn from experimental results The conclusions drawn from experimental results may not accurately reflect hat has gone on in may not accurately reflect hat has gone on in the experiment itselfthe experiment itself


Sources of internal invaliditySources of internal invalidity

These sources often discussed as part of These sources often discussed as part of experiments, but can be applied to all experiments, but can be applied to all designs (e.g. see reactivity)designs (e.g. see reactivity)

HistoryHistory Historical events may occur that will be Historical events may occur that will be

confounded with the IVconfounded with the IV Especially in field research (compare the Especially in field research (compare the

control in a laboratory, e.g. nonsense syllables control in a laboratory, e.g. nonsense syllables in memory studiesin memory studies


MaturationMaturation

Changes over time can be caused by a Changes over time can be caused by a natural learning processnatural learning process

People naturally grow older, tired, bored, People naturally grow older, tired, bored, over timeover time


Testing (reactivity)Testing (reactivity)

People realize they are being studied, and People realize they are being studied, and respond the way they think is appropriaterespond the way they think is appropriate

The very act of studying something may The very act of studying something may change itchange it

In qualitative research, the "on stage" In qualitative research, the "on stage" effectseffects


The Hawthorne studiesThe Hawthorne studies

Improved performance because of the Improved performance because of the researcher's presence - people became researcher's presence - people became aware that they were in an experiment, or aware that they were in an experiment, or that they were given special treatmentthat they were given special treatment

Especially for people who lack social Especially for people who lack social contacts, e.g. residents of nursing homes, contacts, e.g. residents of nursing homes, chronic mental patientschronic mental patients


Placebo effectPlacebo effect

When a person expects a treatment or When a person expects a treatment or experience to change her/him, the person experience to change her/him, the person changes, even when the "treatment" is changes, even when the "treatment" is know to be inert or ineffectiveknow to be inert or ineffective

Medical researchMedical research "The bedside manner", or the power of "The bedside manner", or the power of

suggestionsuggestion


Experimenter expectancyExperimenter expectancy

Pygmalion effect - self-fulfilling prophecies of Pygmalion effect - self-fulfilling prophecies of e.g. teachers' expectancies about student e.g. teachers' expectancies about student achievementachievement

Experimenters may prejudge their results - Experimenters may prejudge their results - experimenter biasexperimenter bias

Double blind experiments:Double blind experiments: Both the researcher and the research participant Both the researcher and the research participant

are "blind" to the purpose of the study.are "blind" to the purpose of the study. They don't know what treatment the participant They don't know what treatment the participant

is gettingis getting


InstrumentationInstrumentation

Instruments with low reliability lead to Instruments with low reliability lead to inaccurate findings/missing phenomenainaccurate findings/missing phenomena

e.g. human observers become more e.g. human observers become more skilled over time (from pretest to posttest) skilled over time (from pretest to posttest) and so report more accurate scores at and so report more accurate scores at later time pointslater time points


Statistical regression to the meanStatistical regression to the mean

Studying extreme scores can lead to Studying extreme scores can lead to inflated differences, which would not inflated differences, which would not occur in moderate scorersoccur in moderate scorers


Selection biasesSelection biases

Selection subjects for the study, and Selection subjects for the study, and assigning them to E-group and C-groupassigning them to E-group and C-group

Look out for studies using volunteersLook out for studies using volunteers


AttritionAttrition

Sometimes called experimental (or Sometimes called experimental (or subject) mortalitysubject) mortality

If subjects drop out, it creates a bias to If subjects drop out, it creates a bias to those who did notthose who did not e.g. comparing the effectiveness of family therapy with e.g. comparing the effectiveness of family therapy with

discussion groups for treatment of drug addictiondiscussion groups for treatment of drug addiction addicts with the worst prognosis more likely to drop out of the addicts with the worst prognosis more likely to drop out of the

discussion groupdiscussion group will make it look like family therapy does less well than will make it look like family therapy does less well than

discussion groups, because the "worst cases" were still in the discussion groups, because the "worst cases" were still in the family therapy groupfamily therapy group


Diffusion or imitation of treatmentsDiffusion or imitation of treatments

When subject can communicate to each When subject can communicate to each other, pass on some information about the other, pass on some information about the treatment (IV)treatment (IV)


CompensationCompensation

In real life, people may feel sorry for C-In real life, people may feel sorry for C-group who does not get "the treatment" - group who does not get "the treatment" - try to give them something extratry to give them something extra e.g. compare usual day care for street e.g. compare usual day care for street

children with an enhanced day treatment children with an enhanced day treatment conditioncondition

service providers may very well complain service providers may very well complain about inequity, and provide some enhanced about inequity, and provide some enhanced service to the children receiving usual careservice to the children receiving usual care


Compensatory rivalryCompensatory rivalry

C-group may "work harder" to compete C-group may "work harder" to compete better with the E-groupbetter with the E-group


DemoralizationDemoralization

Opposite to compensatory rivalryOpposite to compensatory rivalry May feel deprived, and give upMay feel deprived, and give up

e.g. giving unemployed high school dropouts e.g. giving unemployed high school dropouts a second chance at completing matric via a a second chance at completing matric via a special education programmespecial education programme

if we assign some of them to a control if we assign some of them to a control group, who receive "no treatment", they group, who receive "no treatment", they may very well become profoundly may very well become profoundly demoralizeddemoralized


External validityExternal validity

Can the findings of the study be Can the findings of the study be generalized?generalized?

Do they speak only of our sample, or of a Do they speak only of our sample, or of a wider group?wider group?

To what populations, settings, treatment To what populations, settings, treatment variables (IV's), and measurement variables (IV's), and measurement variables can the finding be generalized?variables can the finding be generalized?



Mainly questions about three aspects:Mainly questions about three aspects: Research participantsResearch participants Independent variables, or manipulationsIndependent variables, or manipulations Dependent variables, or outcomesDependent variables, or outcomes

Says nothing about the truth of the result that Says nothing about the truth of the result that we are generalizingwe are generalizing

External validity only has meaning once the External validity only has meaning once the internal validity of a study has been establishedinternal validity of a study has been established

Internal validity is the basic minimum without Internal validity is the basic minimum without which an experiment is uninterpretablewhich an experiment is uninterpretable



Our interest in answering research questions is rarely Our interest in answering research questions is rarely restricted to the specific situation studied - our interest is restricted to the specific situation studied - our interest is in the variables, not the specific details of a piece of in the variables, not the specific details of a piece of researchresearch

But studies differ in many ways, even if they study the But studies differ in many ways, even if they study the same variables:same variables: operational definitions of the variablesoperational definitions of the variables subject population studiedsubject population studied procedural detailsprocedural details observersobservers settingssettings

Generally bigger samples with valid measures lead to Generally bigger samples with valid measures lead to better external validitybetter external validity


Sources of external invaliditySources of external invalidity

Subject selection - Selecting a sample which Subject selection - Selecting a sample which does not represent the population well, will does not represent the population well, will prevent generalizationprevent generalization

Interaction between the testing situation and the Interaction between the testing situation and the experimental stimulusexperimental stimulus

When people have been sensitized to the issues When people have been sensitized to the issues by the pre-testby the pre-test

Respond differently to the questionnaires the Respond differently to the questionnaires the second time (post-test)second time (post-test)

Operationalization Operationalization


OperationalizationOperationalization

We take a variable with wide scope and We take a variable with wide scope and operationalize it in a narrow fashionoperationalize it in a narrow fashion

Will we find the same results with a Will we find the same results with a different operationalization of the same different operationalization of the same variable?variable?


Field experimentsField experiments

"natural" - e.g. disaster research"natural" - e.g. disaster research Static-group comparison type Static-group comparison type Non-equivalent experimental and control Non-equivalent experimental and control

groupsgroups


Strengths and weaknessesStrengths and weaknesses

StrengthsStrengths ControlControl Manipulating the IVManipulating the IV Sorting out extraneous variablesSorting out extraneous variables

Weaknesses Weaknesses Articifiality - a generalization problemArticifiality - a generalization problem ExpenseExpense Limited range of questionsLimited range of questions


IN CONCLUSIONIN CONCLUSION

Donald Campbell often cited Neurath's Donald Campbell often cited Neurath's metaphor:metaphor: "in science we are like sailors who must repair "in science we are like sailors who must repair

a rotting ship while it is afloat at sea. We a rotting ship while it is afloat at sea. We depend on the relative soundness of all other depend on the relative soundness of all other planks while we replace a particularly weak planks while we replace a particularly weak one. Each of the planks we now depend on one. Each of the planks we now depend on we will in turn have to replace. No one of we will in turn have to replace. No one of them is a foundation, nor point of certainty, them is a foundation, nor point of certainty, no one of them is incorrigible"no one of them is incorrigible"

Technology

Types of research design experiments