Adaptive Blinded Sample Size Adjustment for Comparing Two Normal Means: A Mostly Bayesian Approach

• Activity Number: 516
• Type: Contributed
• Date/Time: Wednesday, August 3, 2011 : 10:30 AM to 12:20 PM
• Sponsor: Biopharmaceutical Section
• Author(s): Andrew Montgomery Hartley*+
• Companies: PPD
• Keywords: clinical trials ; adaptive designs ; sample size re-estimation ; bayesian analysis

Abstract

Adaptive sample size re-determination (SSR) for clinical trials consists of examining early subsets of on-trial data, so as to adjust prior estimates of statistical parameters and sample size requirements. Blinded SSR, in particular, while in use already, seems poised to proliferate even further, due to recent draft guidance from the U.S. Food and Drug Administration. On the other hand, current blinded SSR methods offer little to no new information about the treatment effect (TE); the obvious resulting problem is that the TE estimate scientists might simply "plug in" to the SS formulae could be severely wrong. This paper proposes a blinded SSR method which formally synthesizes sample data with prior knowledge about the TE and the variance. It evaluates the method in terms of the average absolute deviation from the targeted statistical power, the type 1 error rate, the bias of the estimated TE and other measures. Under the conditions considered, the method reduces that average absolute deviation by roughly 15% to 25%, relative to another, established method. Simulations show the method to induce minimal bias and no increase to the type 1 error rate.