The Cochran-Mantel-Haenszel statistic is a statistical method used to assess the association between two categorical variables while controlling for a third variable. It is particularly useful in stratified analysis, where data is divided into different groups or strata. This approach helps to eliminate confounding effects and provides a clearer understanding of the relationship between the primary variables. This statistic combines information from multiple 2x2 contingency tables, allowing researchers to analyze data from different studies or groups simultaneously. By calculating a weighted average of the odds ratios, the Cochran-Mantel-Haenszel statistic offers a more robust estimate of the association, enhancing the reliability of the results.