Evaluating clinical significance through equivalence testing: Extending the normative comparisons approach

The field of psychology, as with many other disciplines, has been increasingly interested in being able to measure the effectiveness of behavioral interventions. This trend has led to a number of different approaches for measuring clinical significance, each addressing a slightly different aspect of the clinical outcome. Recently, clinical psychologists (and clients) have supported the contention that one of the most important therapeutic questions is whether clients are functioning equivalently to normal controls following an intervention. To address this question, Kendall, Marrs-Garcia, Nath, and Sheldrick (1999) presented an approach to measuring clinical significance that utilizes tests of equivalence. The present study clarifies the nature of the hypotheses being conducted in measuring clinical significance with tests of equivalence and extends the approach by incorporating recent advances in equivalence testing. A revised approach for evaluating clinical significance via equivalence testing is proposed, and an empirical example demonstrating this approach is provided.