Interpreting results of single-subject research designs

Although single-subject research design has been discussed at some length in the recent physical therapy and occupational therapy literature, there has been little attempt to describe the procedures used for interpreting the experimental effects of such research. The purpose of this paper is to present the use of two strategies for determining whether changes have occurred as a result of experimental manipulation. The first strategy, visual analysis of graphed data, relies on visual interpretation of changes in data patterns both within and between experimental conditions. The second strategy is the use of statistical procedures such as trend estimation, the Rn statistic, and time series analysis. Finally, the issues of both clinical and statistical significance in interpreting the results of single-subject research are discussed.