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Internal Validity

Internal Validity. Internal Validity. All about whether the research design (and data analysis) warrants the conclusions. Concerned with: Causal relationships Various threats to internal validity Single group Multiple group Social effects Experimenter effects. Causal Relationships.

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Internal Validity

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  1. Internal Validity

  2. Internal Validity • All about whether the research design (and data analysis) warrants the conclusions. • Concerned with: • Causal relationships • Various threats to internal validity • Single group • Multiple group • Social effects • Experimenter effects

  3. Causal Relationships • Three conditions are needed to establish a casual relationship: • Temporal condition: Presumptive cause must precede the effect. • Statistical relationship between cause and effect. • Correlation • t test, ANOVA, or other statistical test of a null hyp. • Elimination of plausible alternative explanations. • This is usually the most difficult to esbablished.

  4. Plausible Alternative Explanations • Single group threats Posttest only design: X--------------->O or Prettest-postest design: O-------X------>O Note X is a treatment O is an observation or measurementThreats include: History, maturation, testing, instrumentation, mortality, regression (to the mean)

  5. Plausible Alternative Explanations • Multiple group threats Typically involve interactions of single-group threats and selection (of participants). Selection-history Selection-maturation Selection-testing Selection-instrumentation Selection-regression

  6. Social Effects • Effects that result from social interaction Diffusion of treatment Imitation of treatment Compensatory Rivalry (John Henry Effect) Resentful Demoralization

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