2. QUASI-EXPERIMENTS w Compare subjects in different conditions on a DV w Lacks one or more criteria for an experiment (cause, comparison, control) w Interpreted like a correlational study

3. Why Do Quasi-Experiments? w Internal validity is a problem because the IV is not manipulated w It may not be possible or ethical to manipulate the IV

4. Ex Post Facto Designs w Compare groups that differ on a pre- existing variable (subject variable) w Examples: gender personality presence of mental disorder

5. One-Group Posttest Only Design w Scores are measured after a treatment for one group w The treatment is not manipulated, and there is no comparison

6. One-Group Pretest-Posttest Design w Scores are measured before and after an event or treatment w The treatment is not manipulated

7. Non-Equivalent Control Group Design w Compare a treatment group and a control group before and after the treatment w The groups are not randomly assigned

8. Single Group Time Series Design w Scores are measured several times before and after an event or treatment w Better than Pretest-Posttest design, because you can tell whether the change is likely to be due to a random fluctuation

9. Multiple Time Series Design w Scores for a treatment and control group are measured several times before and after w The control group is not randomly assigned w Combination of Nonequivalent Control Group and Interrupted Time Series

10. Cross-Sectional Design w Compare different age groups at one point in time w The groups may differ on other variables, since age is not manipulated w cohort effects - generational history differences

11. Longitudinal Design w Measure the same group at different ages w Time-consuming w Attrition can be a problem

12. Cohort Design w Compare different age groups at different ages w Combination of longitudinal and cross- sectional

13. Statistics for Quasi-Experiments w Choose from the same set of statistics used for experiments w Remember that you interpret differences like the study was correlational w Take into account number of conditions and whether variables are between or within subjects