Power and Sample Size Calculations in Clinical Trials with Patient-Reported Outcomes under Equal and Unequal Group Sizes Based on Graded Response Model: A Simulation Study

It is crucial to use an adapted sample size formula in a GRM-based analysis because the classical formula designed for the CTT-based approach does not consider the impact of the number of items, which could result in an inadequately sized study and a decrease in power. Thus, when clinicians design a randomized clinical trial with polytomous PRO endpoints using classical sample size formula as the base, they should be aware of the possibility of making an incorrect clinical decision.