A SAS macro for sample size adjustment and randomization test for internal pilot study.

An unnecessarily high or inadequately low sample size often occurs in clinical trials if the planned variance of the trials is overestimated or underestimated. Internal pilot study which utilizes the information from the patients recruited up to interim stage can solve this problem well by re-estimating the variance and re-calculating the sample size. The trial may get a satisfactory power but the type I error rate may be inflated while the t-test is adopted to make hypothesis test because condition of t-distribution is not sufficed any more with variation of the sample size resulted from internal pilot design. If blind variance estimators of the internal pilot are used for sample size recalculation and randomization test is used to accomplish the final hypothesis test, not only the blindness of the internal pilot is preserved but also the ability to control the type I error rate is guaranteed. A SAS macro is programmed to simulate the process of sample size adjustment and randomization test.