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A pre-post design is a method for assessing the impact of an intervention by comparing scores on a variable before and after an intervention occurs. The simplest type of this design involves one group—for example, program participants in a summative evaluation. Validity of the design is enhanced by adding a control group whose members do not experience the intervention and by randomly assigning persons to treatment and control conditions. The more valid the design, the greater the confidence of the evaluator in making decisions about the efficacy of an intervention.

Joseph M. Petrosko
Further Reading
Shadish, W. R., Cook, T. D., & Campbell, D. T.(2002)Experimental and quasi-experimental designs for generalized causal inference. New York: Houghton Mifflin.
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