Bivariate Zero-Inflated Poisson Populations: Statistical Test for Homogeneity

The theme of this entry is on the discussion of the testing of treatment difference in the occurrence of a study end point. In particular, a randomized parallel-group comparative clinical trial with repeated responses under the assumption that the responses follow a bivariate zero-inflated Poisson (ZIP) distribution is considered.
Result based on likelihood ratio test for homogeneity of two bivariate ZIP populations is presented. Approximate formula for sample size calculation is also obtained, which achieves a desired power for detecting a clinically meaningful difference under an alternative hypothesis. An example concerning the comparison
of treatment effect in an addictive clinical trial in terms of the number of days of illicit drug use during a month is given for illustration purpose.