# QUASI-EXPERIMENTS What is a Quasi-Experiment?

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QUASI-EXPERIMENTS What is a Quasi-Experiment?
What is a Single-Group Time Series Design? Why Do Quasi-Experiments? What is a Multiple-Group Time Series Design? What is an Ex Post Facto Design? What is a Cross-Sectional Design? What is a Single-Group Posttest Only Design? What is a Longitudinal Design? What is a Single-Group Pretest/Posttest Design? What is a Sequential or Cohort Design? What is a Nonequivalent Control Group Pretest/Posttest Design? How Are Quasi-Experiments Analyzed?

What is a Quasi-Experiment?
Compare subjects in different conditions on a DV Lacks one or more criteria for an experiment (cause, comparison, control) Interpreted like a correlational study

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

What is an Ex Post Facto Design?
Compare groups that differ on a pre-existing variable (subject variable) Examples: gender personality presence of mental disorder

What is a Single-Group Posttest Only Design?
Scores are measured after a treatment for one group The treatment is not manipulated, and there is no comparison

What is a Single-Group Pretest-Posttest Design?
Scores are measured before and after an event or treatment The treatment is not manipulated

What is a Non-Equivalent Control Group Pretest/Posttest Design?
Compare a treatment group and a control group before and after the treatment The groups are not randomly assigned

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

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

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

What is a Longitudinal Design?
Measure the same group at different ages Time-consuming Attrition can be a problem

What is a Sequential or Cohort Design?
Compare different age groups at different ages Combination of longitudinal and cross-sectional

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