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A Paradox of Power

Arch Gen Psychiatry. 2000;57:329-330.

	Since this article does not have an abstract, we have provided the first 150 words of the full text and any section headings.

IN THIS issue, Khan et al¹ examine extensive randomized clinical trial data from the Food and Drug Administration (Washington, DC), looking at differences between placebo and active medications in antidepressant trials. They found that relative to subjects receiving investigational or other active comparator antidepressants, those receiving placebo had smaller reductions in symptoms, but no differences in rates of suicide attempts or completions.¹ Here I shift from adverse effects of placebo to describe a benefit of including placebo in a clinical trial.

My discussion is based on a fundamental aspect of study design: the inverse relationship between the study sample size and the population effect size that is detectable. I will show that if an investigational drug is initially evaluated in a placebo-controlled trial, the number of subjects that must be enrolled is relatively small and, consequently, the number of nonresponders is small. In contrast, because smaller differences would be expected . . . [Full Text of this Article]

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