Count Data Analysis in Randomised Clinical Trials

Choosing the best model for analysis of count data in randomised clinical trials is complicated. In this paper, we review count data analysis with different parametric and non-parametric methods used in randomised clinical trials, and we define procedures for choosing between the two methods and their subtypes. We focus on analysis of simple count data and do not consider methods for analyzing longitudinal count data or Bayesian statistical analysis. We recommend that: (1) a detailed statistical analysis plan is published prior to access to trial data; (2) if there is lack of evidence for a parametric model, both non-parametric tests (either the van Elteren test or the Tadap2 test, based on an aligned rank test with equal stratum weights) and bootstrapping should be used as default methods; and (3) if more than two intervention groups are compared, then the Kruskal–Wallis test may be considered. If our recommendations are followed, the risk of biased results ensuing from analysis of count data in randomised clinical trials is expected to decrease.