Transcription of Sample Size Calculations for Randomized Controlled Trials
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Sample Size Calculations for Randomized Controlled Trials
Sample size Calculations for Randomized Controlled TrialsJanet WittesINTRODUCTIONMost informed consent documents for Randomized con-trolled Trials implicitly or explicitly promise the prospectiveparticipant that the trial has a reasonable chance of answer-ing a medically important question. The medical literature,however, is replete with descriptions of Trials that providedequivocal answers to the questions they addressed. Papersdescribing the results of such studies may clearly imply that thetrial required a much larger Sample size to adequately addressthe questions it posed. Hidden in file drawers, undoubtedly, aredata from other Trials whose results never saw the light ofday some, perhaps, victims of inadequate Sample size . Al-though many inadequate-sized studies are performed in a sin-gle institution with patients who happen to be available, someare multicenter Trials designed with overly optimistic assump-tions about the effectiveness of therapy, too high an estimate ofthe event rate in the control group, or unrealistic assumptionsabout follow-up and this review, I discuss statistical considerations in thechoice of Sample size and statistical power for randomizedcontrolled trial
An example from a hypothetical controlled trial that tests the effect of a therapy on levels of high density lipoprotein (HDL) cholesterol is used to illustrate each case. Having introduced a basic formula for sample size, the review discusses each element of the formula in relation to its applicability to controlled trials and then points to ...
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