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. Depression in rape victims
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. Longitudinal design
TIME
Generations
Timespan of research

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

6. Cross-sectional research
TIME
Generations
Timespan of 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. Cohort-sequential research
TIME
Generations
Timespan of 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
Average IQ
Cross-sectional
Age