This note is motivated by recent works of Xie et al. (2009) and Xiang et al. (2007). Herein, we simplify the score statistic presented by Xie et al. (2009) to test overdispersion in the zero-inflated generalized Poisson (ZIGP) mixed model, and discuss an extension to test overdispersion...

We present new Stata commands for carrying out exact Wilcoxon one-sample and two-sample comparisons of the median. Nonparametric tests are often used in clinical trials, in which it is not uncommon to have small samples. In such situations, researchers are accustomed to making inferences by...

We present motivation and new Stata commands for modeling count data. While the focus of this article is on modeling data with underdispersion, the new command for fitting generalized Poisson regression models is also suitable as an alternative to negative binomial regression for overdispersed data.