.I. Behov. Ther. &Exp. Psychiar. Vol. 14, No.4, pp. 311-315, 1983. Printed in Great Britain. CCC&7916/83$3.CCI+ .OO 0 1983 Pergamon Press Ltd. THE REPEATED PRETEST-POSTTEST SINGLE-SUBJECT EXPERIMENT: A NEW DESIGN FOR EMPIRICAL CLINICAL PRACTICE* BRUCE A. THYER and GEORGE C. CURTIS The University of Michigan Summary-The logic of a new design for empirical clinical practice, the repeated pretest-posttest experiment, is described. This design is readily applicable by individual practitioners in the human services, possesses high internal validity, and presents minimal intrusiveness into the delivery of service. A single-case study is used to illustrate the application of the repeated pretest-posttest experiment in clinical research. Single-case experimental designs have gained increasing acceptance as a valuable tool for research and development in the human services. Numerous sources describe the application of such designs in the fields of psychiatry (Liberman et al., 1973), psychology (Hersen and Barlow, 1976), social work (Jayaratne and Levy 1979), education (Blackman and Silberman, 1975), and nursing (LeBow, 1975). Unfortu- nately, despite the widespread dissemination of single-case experimental methodology, the designs are not widely employed at the level of the individual practitioner in these disciplines. A number of reasons have been advocated to explain this phenomenon but what is perhaps the most significant drawback to the clinical employ- ment of single-subject research strategies is the fact that those designs which are most readily applied by the individual practitioner typicall: possess rather low levels of internal validity (Thomas, 1978). Those designs with the potential for high internal validity often present too many constraints on the delivery of effective service (i.e. extended or multiple baselines, reversal or withdrawal phases). What is needed to facilitate the application of single-subject research methodology is the development of experimental designs of high internal validity which are easily applicable in the service setting. A number of steps have been taken in this direction. See, for example, the designs described by Watson and Workman (1981), and by Barlow and Hayes (1979). The present study describes the experi- mental logic and application of another such design, the repeated pretest-posttest single case experiment. DESCRIPTION AND EXPERIMENTAL LOGIC OF THE DESIGN The traditional AB design employs repeated measures of the subject’s behavior over two time periods, a baseline phase and during intervention. If visually significant changes are detected, a treatment effect may be inferred. Other factors which may give rise to changes in the client which are not excluded by this design include, among others, the threats of concurrent history, matura- tion, testing, physical changes, regression and drug use. Even with the best of data obtained from AB designs the practitioner rarely has *Portions of this paper were presented at the annual meeting of the Association for Behavior Analysis, Milwaukee, Wisconsin, May 27-31 1982. Address all correspondencetoBruceA.Thyer, Ph.D., Anxiety Disorders Program, Adult Psychiatric Hospital, The University of Michigan, Ann Arbor, MI 48109, U.S.A. 311