Comparative Post-test Design
Comparison post-test design is a quasi-experimental design that involves the measurement of outcomes for both the test group as well as a comparison group. The selection of participants into the treatment and comparison groups is not done randomly. While such a design to some extent overcomes the issues of a one-shot study by allowing comparisons of success, this design is typically plagued by threats due to selection bias. That is, an alternate explanation for differences between group outcomes is that some alternate factor, which was related to the selection process, has actually caused the differences in outcomes.
US Environmental Protection Agency. (2007). Program Evaluation Glossary. Office of the Administrator/Office of Policy/Office of Strategic Environmental Management/Evaluation Support Division.