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Letters
November 6, 2002

The Ethics of Underpowered Clinical Trials—Reply

JAMA. 2002;288(17):2118-2119. doi:10.1001/jama.288.17.2118

In Reply: Dr Janosky correctly points out that statistical power is a continuous quantity. Accepting the value of .80 as adequate power is as arbitrary as accepting .05 to denote statistical significance. Greater power and stricter standards for significance will always be preferable, but one is always obtained at the cost of the other. Our experience has been that many peer reviewers still adhere to a dichotomy based on 80% or 90% power. However, no numerical value for power will be adequate if it is generated without carefully considering the size of the clinically important effect. The 3-tiered model we propose may help investigators determine such effects and calculate their power accordingly.

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