"In statistics, the Cochran--Mantel--Haenszel test (CMH) is a test used in the analysis of stratified or matched categorical data. It allows an investigator to test the association between a binary predictor or treatment and a binary outcome such as case or control status while taking into account the stratification. It is often used in observational studies where random assignment of subjects to different treatments cannot be controlled, but confounding covariates can be measured. The extensions to the Cochran--Mantel--Haenszel (CMH) tests and the nonparametric analysis of variance (NP ANOVA) methodology provide powerful new statistical tests that enable deeper data analysis."-- Provided by publisher.