Sequential testing example7/1/2023 ![]() ![]() The accumulated information report shows the number of individuals that should be included at each look. The average sample size given the alternative hypothesis is lower than the required sample size, since a considerable number of simulated studies terminate early for efficacy. The report shows the achieved power and alpha values, as well as the required sample size. The simulation process takes a few moments to complete. We press the Calculate button to run the simulation and generate the report. One of the more common choices is the O’Brien-Fleming alpha spending function, which spends very little alpha in early looks and preserves the larger portion of alpha for the later looks. The alpha spending function defines the portion of alpha that is spent at each look. We will specify 5 equally spaced looks, so that there are 4 interim looks and a final look. Since the test is two-sided, there are not options for futility boundaries. On the Looks and Boundaries tab, there are options for customized specification of the look details, or a simple specification may be used. We wish to base the calculations on a standard deviation of 4.7. We wish to have equal sample sizes in each group.įor the control group, we assume the population mean to be 36.8.įor the treatment group, we assume the population mean to be 41.4. We set the desired power to 0.9 and alpha to 0.05. ![]() Typically, one hundred thousand or more simulations should be used, but we will use twenty thousand for the sake of time. We will solve for Sample Size for a two-sided T-test. In this example, we will assume that the underlying data distributions of the two groups are Normal, so we will open the Group-Sequential Tests for Two Means Assuming Normality procedure. The early looks allow the study to be terminated early if there is sufficiently strong early evidence of efficacy, or, if the design permits, for futility. Interim looks are early analyses after only a portion of the data has been collected. Group-sequential testing is used to permit interim looks during the course of a study. We will also generate the boundaries for each look. In this video, we will briefly explore estimating the sample size for a group-sequential test for comparing two means.
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