A More Rigorous QUASI-Experimental Alternative to the One-Group Pretest-Posttest Design

Abstract

A simple quasi-experimental design is described which may have utility in a variety of applied and laboratory research settings where ordinarily the one-group pretest-posttest pre-experimental design might otherwise be the procedure of choice. The design achieves high levels of internal and external validity and produces independent control groups by independently randomly assigning subjects to measurement occasions. It has superior internal and external validity in comparison with the one-group pretest-posttest design, in particular, but also in comparison with a number of other designs. The design includes elements which help control the internal validity factors-history, maturation, testing, regression, selection and their interactions; and the external validity factors-interaction of testing and treatment, interaction of selection and treatment, reactive arrangements and multiple treatment interference. The design approaches the internal validity of true experimental designs while optimizing external validity. It is readily analyzable with ANOVA techniques. The design may be particularly appropriate for evaluations of ongoing instructional programs in the schools, or evaluations of programmatic interventions or therapies occuring on an ongoing basis.