Uncommon but Dramatic Responses to Treatment

Abstract

Large effects in moderate to large studies are typically insensitive to small and moderate unobserved biases, but the concept of a ‘large effect’ is vague. What if most subjects are not much affected by treatment, but a small fraction, perhaps 10% or 20% of subjects, are strongly affected? On average, such an effect may be small, but not at all small for the affected fraction. Is such an effect insensitive to small and moderate unobserved biases?