Effect size as a measure of symptom-specific drug change in clinical trials.

A data-analytic strategy is proposed for identifying the symptom-specific effects of each medication in a clinical trial. The within-group effect size is a standardized ratio of the pre-post change relative to the stability of change for each treatment group. Advantages of using this descriptive approach are illustrated by examining antidepressant effects of alprazolam, imipramine, and placebo in a clinical trial for patients meeting criteria for both panic disorder and depression. There was a significant difference between active medication and placebo on the Hamilton Rating Scale for Depression (HAM-D) total, but no difference between the anti-depressant effects of the active medications despite their diverse psychopharmacologic properties. Examination of effect sizes for each HAM-D item revealed distinct symptom-specific effects of each active medication in this study sample. Although these descriptive findings cannot be used for inferential conclusions, they can be used to guide the design of future trials.