Clinical trials are often costly, and time consuming. The ability to get new products into the market early is critical to the success of pharmaceutical and medical device companies. Most practitioners use Fisher's exact tests to determine the required sample size for testing efficacy rates. We shall argue that when the sample size is not too small, normal approximation tests should be used instead of Fisher's exact tests. Several different sets of hypotheses and their corresponding formulas to compute sample size for clinical trial based upon normal approximation test are given.
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