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Activity Number: 486
Type: Contributed
Date/Time: Wednesday, August 7, 2013 : 8:30 AM to 10:20 AM
Sponsor: Biopharmaceutical Section
Abstract - #310170
Title: Interim Analysis for the Mean Difference of Two Samples Using Generalized P-Values
Author(s): Richard McNally*+
Companies: Covance
Keywords: Interim analysis ; Group sequential designs ; Generalized p-value ; Generalized fiducial inference ; Student's t distribution
Abstract:

As interest in serious diseases or vulnerable populations has increased, group sequential designs have become more widely used in clinical trials. To accurately determine the p-value when an interim analysis has occurred, one must know the distribution of the final test statistic. Most methods for interim analyses are based on breaking the test statistic into independent increments with a multivariate standard normal distribution. It is assumed that either the variance of the parameter of interest is known or can be estimated with relative certainty. When the variance must be estimated with small samples, one commonly-used method only uses the variance estimate from the first interim analysis to preserve the type I error. Our methodology for the mean difference of 2 independent samples after a single interim analysis has occurred uses generalized p-values (Tsui and Weerahandi, 1989). The generalized test function includes the t statistic used in the first interim analysis and variance estimates from both stages. Our method is compared to existing methods for interim analysis based on the t test. We discuss the extension of this method to trials with more than one interim analysis.


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