Internal Invalidity in Pretest-Posttest Self-Report Evaluations and a Re-evaluation of Retrospective Pretests

摘要

True experimental designs (Designs 4, 5, and 6 ofCampbell & Stanley, 1963) are thought to provideinternally valid results. This paper describes fivestudies involving the evaluation of various treatmentinterventions and identifies a source of internalinvalidity when self-report measures are used ina Pretest-Posttest manner. An alternative approach(Retrospective Pretest-Posttest design) to measuringchange is suggested, and data comparing its accuracywith the traditional Pretest-Posttest designin measuring treatment effects is presented. Finally,the implications of these findings for evaluation researchusing self-report instruments and thestrengths and limitations of retrospective measuresare discussed.