  We propose BaySize, a sample size calculator for phase I clinical trials
using Bayesian models. BaySize applies the concept of effect size in dose
finding, assuming the MTD is defined based on an equivalence interval.
Leveraging a decision framework that involves composite hypotheses, BaySize
utilizes two prior distributions, the fitting prior (for model fitting) and
sampling prior (for data generation), to conduct sample size calculation under
desirable statistical power. Look-up tables are generated to facilitate
practical applications. To our knowledge, BaySize is the first sample size tool
that can be applied to a broad range of phase I trial designs.
