The relation of patients' treatment preferences to outcome in a randomized clinical trial.

Randomization procedures are performed in order to maximize the internal validity of treatment outcome studies. Objections have been made that this practice undermines the external validity of these studies because it ignores patients' treatment preferences, thereby precluding the self-selection of treatment that can occur in the community. This study used data from a multisite, double-blind, randomized, placebo-controlled trial comparing antidepressant medication to cognitive therapy for moderately to severely depressed outpatients. It compared the treatment outcomes of patients who, via randomization, received their preferred treatment versus those who did not. Although the majority of patients stated a preference for one treatment over the other, there was no significant difference in the magnitude of reduction in symptoms of depression between those who received their treatment of choice versus those who did not. These results do not provide support for the claim that the external validity of randomized controlled trials suffers from this aspect of the randomization procedure.