Internal invalidity in pretest-posttest self-report evaluations and a re-evaluation of retrospective pretests.

Abstract

True experimental designs (Designs 4, 5, and 6 of Campbell & Stanley, 1963) are thought to provide internally valid results. This paper describes five studies involving the evaluation of various treatment interventions and identifies a source of internal invalidity when self-report measures are used in a Pretest-Posttest manner. An alternative approach (Retrospective Pretest-Posttest design) to measuring change is suggested, and data comparing its accuracy with the traditional Pretest-Posttest design in measuring treatment effects is presented. Finally, the implications of these findings for evaluation research using self-report instruments and the strengths and limitations of retrospective measures are discussed.