Mala Mahadevan explains the Cochran-Mantel-Haenszel test, with two parts up so far. First, her data set:

Below is the script to create the table and dataset I used. This is just test data and not copied from anywhere.

Second, an introduction to the test itself and solutions in R and T-SQL:

This test is an extension of the Chi Square test I blogged of earlier. This is applied when we have to compare two groups over several levels and comparison may involve a third variable.

Let us consider a cohort study as an example – we have two medications A and B to treat asthma. We test them on a randomly selected batch of 200 people. Half of them receive drug A and half of them receive drug B. Some of them in either half develop asthma and some have it under control. The data set I have used can be found here. The summarized results are as below.

This series is not yet complete, so stay tuned.