Sample-Size Calculation for Comparing Two Negative Binomial Rates

• Activity Number: 536
• Type: Contributed
• Date/Time: Wednesday, August 7, 2013 : 10:30 AM to 12:20 PM
• Sponsor: Biopharmaceutical Section
• Author(s): Haiyuan Zhu*+ and Hassan Lakkis
• Companies: Forest Research Laboratories and Forest Research Laboratories
• Keywords: Negative binomial model ; Sample size ; Power ; Count data

Abstract

Negative binomial model has been increasingly used to model count data in recent clinical trials. It is frequently chosen over Poisson model in cases of over-dispersed count data that is commonly seen in clinical trials. An important challenge of applying negative binomial approach in clinical trial design is sample size estimation. In practice, simulation methods have been frequently used to estimate the sample size. In this paper, an explicit formula is developed to calculate sample size for comparing two negative binomial rates. Depending on different approaches to estimate the variance under null hypothesis, three variations of the sample size formula are proposed and their performances are assessed using simulations.