Planning a Randomized Trial

Summary: A critical component of any well-conceived clinical trial is an estimate of the total sample size. Many clinical trials are limited by small sample sizes that increase the risk of false-negative conclusions. This article describes how to calculate a sample size in the planning phase of a clinical trial and lays out the rationale behind the parameters of the sample size calculation with an emphasis on avoiding type II (beta) errors. The reporting of sample size estimates is presented in the context of a grant proposal.