Single-arm studies are typically used in phase II of clinical trials, whose main objective is to determine whether a new treatment warrants further testing in a randomized phase III trial. The introduction of randomization in phase II, to avoid the limits of studies based on historical controls, is a critical issue widely debated in the recent literature. We use a Bayesian approach to compare single-arm and randomized studies, based on a binary response variable, in terms of their abilities of reaching the correct decision about the new treatment, both when it performs better than the standard one and when it is less effective. We evaluate how the historical control rate, the total sample size, and the elicitation of the prior distributions affect the decision about which study performs better.
Keywords: Bayesian approach; historical control rate; phase II clinical trials; randomization.