AN INVESTIGATION OF INTERNAL AND EXTERNAL VALIDITY IN SINGLE-SUBJECT EXPERIMENTAL DESIGNS

Abstract

This article discussed methodological issues in research studies using single-subject experimental designs. Examples of different single subject designs employed in applied clinical research are presented and reviewed. Practical issues and problems arising during the execution of research are highlighted. Issues discussed involve internal and external validity that help experimenters determine whether a change in behavior has value for one subject or generalizability for other subjects. Internal validity refers to research design and experimental control, analysis of date, and reliability. One problem occurs when the experimenter fails to provide ample internal replications of the treatment. Another problem is related to the selection of an inappropriate research design. Analysis of data is applied to the stable trend in baseline, and the change in response to the introduction or withdrawal of treatment. External validity, on the other hand, is concerned with clinical significance and generality of the findings. The clinical significance is evaluated from social validation: normative and subjective evaluation. Statements about generalization can be made when specific replications are used. The author suggests guidelines for solving methodological problems and for avoiding their recurrence in single-subject research designs.