Single-subject research in rehabilitation: a review of studies using AB, withdrawal, multiple baseline, and alternating treatments designs.

OBJECTIVE: To review the "methodologic rules" for using single-subject research designs (SSRDs) and to review the use of SSRDs in rehabilitation research of the past decade. DATA SOURCES: CINAHL and MEDLINE searches using "single subject" and "single system" as key words for the period 1985-1995 yielded 61 articles related to rehabilitation. STUDY SELECTION: Studies were selected for review if they described one of four commonly used SSRDs, specifically AB, withdrawal, multiple baseline, or alternating treatments. DATA EXTRACTION: Studies cited were identified by consensus and either exemplify adherence to the experimental rules of SSRDs or illustrate errors that result in threats to the validity of stated findings. DATA SYNTHESIS: All four types of SSRDs have been reported in rehabilitation studies, sometimes incorrectly.
CONCLUSIONS: SSRDs, with their client-centered focus, are ideally suited for researching human behavior in the rehabilitation practice environment. Although numerous sources clearly identify the methodologic requirements for single-subject experiments, several studies violate the basic rules, threatening the validity of the results of these studies. Other properly applied SSRDs illustrate the strengths of this approach, which can produce empirical support for rehabilitation interventions.