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Clinical Trial
, 299 (13), 690-4

The Importance of Beta, the Type II Error and Sample Size in the Design and Interpretation of the Randomized Control Trial. Survey of 71 "Negative" Trials

Clinical Trial

The Importance of Beta, the Type II Error and Sample Size in the Design and Interpretation of the Randomized Control Trial. Survey of 71 "Negative" Trials

J A Freiman et al. N Engl J Med.

Abstract

Seventy-one "negative" randomized control trials were re-examined to determine if the investigators had studied large enough samples to give a high probability (greater than 0.90) of detecting a 25 per cent and 50 per cent therapeutic improvement in the response. Sixty-seven of the trials had a greater than 10 per cent risk of missing a true 25 per cent therapeutic improvement, and with the same risk, 50 of the trials could have missed a 50 per cent improvement. Estimates of 90 per cent confidence intervals for the true improvement in each trial showed that in 57 of these "negative" trials, a potential 25 per cent improvement was possible, and 34 of the trials showed a potential 50 per cent improvement. Many of the therapies labeled as "no different from control" in trials using inadequate samples have not received a fair test. Concern for the probability of missing an important therapeutic improvement because of small sample sizes deserves more attention in the planning of clinical trials.

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