Single-case experimental designs. Evaluating interventions in research and clinical practice.

Single-case designs refer to a methodological approach that can be used to investigate the effectiveness of treatment with the individual client. The designs permit scientifically valid inferences to be drawn about the effects of treatment and hence offer advantages over alternative strategies such as the uncontrolled case study or open study that are used with the individual case. The present article discusses the key features of the methodology, illustrates specific designs and how inferences are drawn, and discusses critical issues (feasibility, generality of results, ethical issues) in the use of the designs. Essential features of the design, including ongoing assessment and drawing on the underlying thinking and logic of the designs can improve the clinical care for individual clients, even when the rigors of experimentation are not feasible or desirable. Lamentably, single-case methods are rarely trained among researchers or practitioners in psychology or related mental health professions. The designs could play a special role by improving individual care and therapeutic change, apart from the strength of the methodology as a purely research tool.