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Chapter 6: The Internal Validity of Research p.157

Chapter 6: The Internal Validity of Research p.157. Confounds Threats to Internal Validity Reactivity Demand Characteristics Experimental Expectancies Summary. Chapter 6: The Internal Validity of Research. Extraneous Variables (so what? Who cares?)

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Chapter 6: The Internal Validity of Research p.157

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  1. Chapter 6: The Internal Validity of Research p.157 • Confounds • Threats to Internal Validity • Reactivity • Demand Characteristics • Experimental Expectancies • Summary

  2. Chapter 6: The Internal Validity of Research • Extraneous Variables (so what? Who cares?) • They contaminate the experiment by providing • Alternative explanations jeopardizing internal validity • i.e. does the experiment test what is says it tests? • Esp. for “training” type studies • Rule them out • Logically (e.g. cohort age differences in early development) • Control for them • random assignment • direct control (e.g. limit them, “females only”) • Measure and estimate their effects on DV • Alternative explanations (2) • Confounds: Two vars cannot be separated; e.g. black females; white males • Artifacts: Something other than the IV is causing changes to DV

  3. Internal Validity: Confounds • Confound: • “when two vars are combined so that the effect of one cannot be separated from the effects of the other” p.156 • ? What are some possible confounding vars in your study? • How to avoid • Untangle them, use each as IV (factorial design) • Eliminate the confound • Selection of Ps • Random assignment (how does that do it?) • Blocking and measuring • Measure the confounding variable

  4. Internal Validity:Confounds • Natural Confounds (Vars that naturally occur together) • Age & maturity; ethnicity & wealth; gender & toy choices • What are some more? • Treatment Confounds • IV is connected with another var or treatment • E.g. female Es conduct exp. Groups; males, control groups • Critical question: • Do Ps experience exactly the same physical, social, temporal environment except for IV? P. 159 • Measurement Confounds • DV measures more than one Hypothetical construct • E.g. depression; anxiety

  5. Internal Validity: Threats (8)Campbell, D. T., & Stanley, J. ‘63 • Time-Related (5) • History • Maturation • Testing • Instrumentation change • Statistical Regression • Selection (3) • Nonrandom assignment • Preexisting groups • Mortality

  6. Internal Threats:Time-Related (5) History: events outside of research setting (e.g. abortion attitudes) Maturation: natural changes over time (e.g. age, experience) Testing: Pretesting effects Instrumentation change: e.g. with experience, E’s assignment to behavioral category Statistical Regression Pre-selection of Ps based on extremes (e.g. anxiety) (see Huck and Sandler, ’79) Air Force cadets

  7. Internal Validity Threats:Control Groups in Pre-Post • Control group equivalence • Random assignment (not a guarantee, though) • Test by pretesting (not needed most of the time) • Important to make sure the pretest is the DV or some measure closely related • Possible to pretest on several measures related to the DV • Can use ANCOVA to remove these effects from DV • Advantages of not using a pretest • Avoid testing effects • Less costly

  8. Internal Validity Threats: Selection Threats • Selection bias:when exp group differs from control group • Non-random assignment • Avoid self-selection (e.g. volunteering) • Avoid data collection bias (collecting one condition first) • How would that cause bias? • Preexisting groups • Ps already self-selected into groups • E.g. work setting: employees more eager for training in trn group • What common characteristics do those in preexisting groups have? • Other examples? • Mortality • Survivors = drop outs?

  9. Internal Validity Threats:Reactivity (ouch!) • Whenever measuring affects DV score • Sources • Evaluation apprehension (judgeaphobia) • Behavior and self-report (faking) • May inhibit or disinhibit behavior (socially desirable responding) • Distraction: • May divert attention from experiment instructions to others • It’s what’s the Participant thinks, not the researcher that’s important • Novelty effects • Participant tries to anticipate what behavior norms should be • E.g. Milgram, S. Asch

  10. Internal Validity Threats:Controlling Reactivity • General control measures: • Hide your identity • don’t call yourself a psychologist! • Be informal, friendly, put them at ease • as much as possible • Distract them • Entertain them • Trick them with deception • Mislead, lie, whatever it takes to diver them

  11. Control Reactivity: • Control with Behavioral Measures • Surreptitious, unobtrusive observation (i.e. candid camera) • Embed IV in environment (Piliavin et al., ’69) • “Waiting room ploy” ?? (Aronson et al., ’90) • Use natural” observers (teachers, parents) • Control with Self-Report Measures • ?? Student evals? Social influence? • Anonymity, confidentiality • Bogus pipeline (Jones & Segall) • Noting Instances of Reactivity

  12. Reactivity: Demand Characteristics (Martin Orne, ’62)“Purposely behaving in ways that affect the outcome of research” p.171 Sources: Participant Roles Good participant Bad participant Apathetic participant Impact of P roles Controlling Demand Cue reduction Motivation Role-play control groups Separate DV measure from study

  13. Threats:Experimenter Expectancies • Types of Experimenter Effects • Biased Observation • Influencing P responses • Techniques of Control • Rehearsal and Monitoring • Minimizing E’s Role • Condition Blindness • Avoidance of Data Snooping

  14. Internal Validity:Summary • Confounds • What are they? • How do you control them? • Threats to Internal Validity • Time related; control groups; selection threats • Reactivity • Evaluation apprehension, Novelty • Controlling reactivity • Demand Characteristics • What is it? How do you control/eliminate them? • Experimental Expectancies • Types: biased observations; influencing Ps responses

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