Y học - Chapter 8: Experimental research

Chapter 8 Experimental ResearchOverview of Experimental ResearchTraditional type of researchPurpose is to investigate cause-and-effect relationships among variablesExperimental groups vs. control groupsEach group of participants receives a different treatmentAlways involves manipulation of the independent variableAnswers the question “What will be?”Systematic ProceduresMore than any other type of research, experimental research should follow a definite, orderly procedureSpecific steps follow . . .Steps in Experimental ResearchState the research problemDetermine if experimental methods applySpecify the independent variable(s)Specify the dependent variable(s)State the tentative hypothesesDetermine measures to be usedPause to consider potential successIdentify intervening (extraneous) variablesFormal statement of research hypothesesDesign the experimentFinal estimate of potential successConduct the study as plannedAnalyze the collected dataPrepare a research reportResearch ValidityInternal Validity – the validity of findings with the research study; the technical soundness of a study, particularly concerned with the control of extraneous influences that might effect the outcomeExternal Validity – the degree to which the findings can be inferred to the population of interest or to other populations or settings; the generalizability of the resultsBoth are important in a study but they are frequently at odds with one another in planning and designing a studyInternal validity is considered the basic minimum for experimental researchInternal Validity. . . this is the basic minimum without which any study is not interpretableParticularly important in experimental studiesDid, in fact, the experimental treatment (X) produce a change in the dependent variable (Y)To answer yes, one must be able to rule out the possibility of other factors producing the changeTo gain internal validity, the researcher attempts to control everything and eliminate possible extraneous influencesLends itself to highly controlled, laboratory settingsThreats to Internal ValidityHistory – events occurring during the experiment that are not part of the treatmentMaturation – biological or psychological processes within participants that may change due to the passing of time, e.g., aging, fatigue, hungerTesting – the effects of one test upon subsequent administrations of the same testInstrumentation – changes in testing instruments, raters, or interviewers including lack of agreement within and between observersThreats continuedStatistical regression – the fact that groups selected on the basis of extreme scores are not as extreme on subsequent testingSelection bias – identification of comparison groups in other than a random mannerExperimental mortality – loss of participants from comparison groups due to nonrandom reasonsInteraction among factors – factors can operate together to influence experimental resultsExternal ValidityGeneralizability of results . . . to what populations, settings, or treatment variables can the results be generalized?Concerned with real-world applicationsWhat relevance do the findings have beyond the confines of the experiment?External validity is generally controlled by selecting subjects, treatments, experimental situations, and tests to be representative of some larger populationRandom selection is the key to controlling most threats to external validityTypes of External ValidityPopulation Validity – refers to the extent to which the results can be generalized from the experimental sample to a defined populationEcological Validity – refers to the extent to which the results of an experiment can be generalized from the set of environmental conditions in the experiment to other environmental conditionsThreats to External ValidityInteraction effects of testing – the fact that the pretest may make the participants more aware of or sensitive to the upcoming treatmentSelection bias – when participants are selected in a manner so they are not representative of any particular populationReactive effects of experimental setting – the fact that treatments in constrained laboratory settings may not be effective in less constrained, real-world settingsMultiple-treatment interference – when participants receive more than one treatment, the effects of previous treatments may influence subsequent onesTypes of DesignsThe basic structure of a research study . . . particularly relevant to experimental researchTypes of designs (Campbell & Stanley, 1963)Pre-experimentalTrue experimentalQuasi-experimentalPre-experimental designsWeak experimental designs in terms of controlNo random samplingThreats to internal and external validity are significant problemsMany definite weaknessesExample: One-group pretest/posttest designTrue experimental designsBest type of research design because of their ability to control threats to internal validityUtilizes random selection of participants and random assignment to groupsExample: Pretest/posttest control group designQuasi-experimental designsThese designs lack either random selection of participants or random assignment to groupsThey lack some of the control of true experimental designs, but are generally considered to be fineExample: Nonequivalent group designMethods of ControlPhysical manipulationSelective manipulationMatched pairs and block designsCounterbalanced designsStatistical techniquesPhysical ManipulationBest way to control extraneous variablesResearcher attempts to control all aspects of the research, except the experimental treatmentDifficult to control all variablesSome variables cannot be physically controlledSelective ManipulationIntent is to increase likelihood that treatment groups are similar at the beginning of studyMatched pairs designParticipants are matched according to some key variable and then randomly assigned to treatment groupBlock design – extension of matched pairs to 3 or more groupsCounterbalanced designAll participants receive all treatments, but in different ordersStatistical TechniquesApplied when physical manipulation or selective manipulation is not possibleDifferences among treatment groups are known to exist at beginning of studyGroups may differ on initial abilityAnalysis of covariance (ANCOVA)Adjusts scores at the end of the study based upon initial differencesCommon Sources of ErrorMany possible sources of error can cause the results of a research study to be incorrectly interpreted. The following sources of error are more specific threats to the validity of a study than those described previouslySelected examples:Hawthorne EffectPlacebo EffectJohn Henry EffectRating EffectExperimenter Bias EffectHawthorne EffectA specific type of reactive effect in which merely being a research participant in an investigation may affect behaviorSuggests that, as much as possible, participants should be unaware they are in an experiment and unaware of the hypothesized outcomePlacebo EffectParticipants may believe that the experimental treatment is supposed to change them, so they respond to the treatment with a change in performanceJohn Henry EffectA threat to internal validity wherein research participants in the control group try harder just because they are in the control groupRating EffectVariety of errors associated with ratings of a participant or groupHalo effectOverrater errorUnderrater errorCentral tendency errorExperimenter Bias EffectThe intentional or unintentional influence that an experimenter (researcher) may exert on a study