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Ex Post Facto research

Ex Post Facto research. Researcher cannot manipulate some variables and therefor selects participants that have certain values for those variables by themselves (gender, personality, illness, ...). Pros Often only possible approach. Cons

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Ex Post Facto research

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  1. Ex Post Facto research • Researcher cannot manipulate some variables and therefor selects participants that have certain values for those variables by themselves (gender, personality, illness, ...) • Pros • Often only possible approach • Cons • Selection threat to internal validity: probably not only independent variable differs among participants

  2. Ex Post Facto - example Depression in rape victims

  3. Research design X1 = rape victim X2 = control Yij = average depression score in group i, at time j ---- indicates possible unequality of groups in both conditions

  4. Generations TIME Timespan of research Longitudinal design

  5. Assess evolution from longitudinal study • Comparison of successive measures of Yi • Experimental loss • Cost • Insensitive to cohort effects

  6. Generations TIME Timespan of research Cross-sectional research

  7. Assess evolution from cross-sectional study • Comparing different measures of Yi(from different groups) • No experimental loss • Fast and cheap • Cohort effects occur but cannot be assessed

  8. Generations TIME Timespan of research Cohort-sequential research

  9. Assess evolution from cohorte-sequential study • Yij = measure at time i in participants of age j • Evolution within cohort is assessed from successive measures Yij • Evolution between cohorts (apart from age) is assessed from comparison between Y1N and Y2N • Experimental loss • Cost • Cohort effects can be assessed

  10. Longitudinal <> Cross-sectional research Intelligence and age Longitudinal Cross-sectional Average IQ Age

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