Chapter 8

  1. Internal validity
    control of confounding and extraneous variables
  2. 11 types of internal validity threats
    • History
    • Selection
    • Maturation
    • Pretesting
    • Instrumentation
    • Treatment replications
    • Subject attrition
    • Statistical regression
    • Diffusion of Treatment
    • Experimenter Effects
    • Subject Effects
  3. History (internal validity threat)
    threat from uncontrolled events that affect the d.v. (external or internal)
  4. Selection (int.val.)
    Threat from the characteristics of the population
  5. Maturation (int.val.)
    Threat from changes in participants over time
  6. Pretesting
    Threat from the effect of taking the pretest
  7. Instrumentation
    threat from unreliability or changes in measurement
  8. Treatment Replications
    • threat from insufficient replications of treatments
    • sometimes number of participants is not the same as number of treatments (if whole group at the same time is receiving the treatment, that's one treatment)
  9. Subject attrition
    Threat from loss of subjects; aka mortality or differential attrition
  10. Statistical regression
    • threat from change of extreme scores to those closer to the mean
    • aka regression twd the mean regression effect, or regression artifact
    • lows and highs on pretest will be higher or lower respectively on posttest
  11. Diffusion of treatment
    threat from treatment effect on one group affecting other groups (that don't receive intervention, or do)
  12. Experimenter Effects
    • threat from characteristics or expectations of the experimenter
    • deliberate or unintentional; treats one group differently because he "wants" that group to do well
  13. Subject effects
    • Threat from effects of awareness of being a subject
    • aka reactivity
    • John Henry ¬†Effect - motivated b/c they didn't get treatment (compensatory rivalry)
    • Hawthorne effect - increase positive/desirable behavior b/c they know receiving special treatment
    • resentful demoralization - didn't get treatment
    • novelty effect - react positively b/c they are doing something new and different
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Chapter 8
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