Example 35.7 Cochran-Mantel-Haenszel Statistics

The data set Migraine contains hypothetical data for a clinical trial of migraine treatment. Subjects of both genders receive either a new drug therapy or a placebo. Their response to treatment is coded as 'Better' or 'Same'. The data are recorded as cell counts, and the number of subjects for each treatment and response combination is recorded in the variable Count.

   data Migraine;
      input Gender $ Treatment $ Response $ Count @@;
      datalines;
   female Active  Better 16   female Active  Same 11
   female Placebo Better  5   female Placebo Same 20
   male   Active  Better 12   male   Active  Same 16
   male   Placebo Better  7   male   Placebo Same 19
   ;

The following PROC FREQ statements create a multiway table stratified by Gender, where Treatment forms the rows and Response forms the columns. The CMH option produces the Cochran-Mantel-Haenszel statistics. For this stratified table, estimates of the common relative risk and the Breslow-Day test for homogeneity of the odds ratios are also displayed. The NOPRINT option suppresses the display of the contingency tables. These statements produce Output 35.7.1 through Output 35.7.3.

   proc freq data=Migraine;
      tables Gender*Treatment*Response / cmh; 
      weight Count;
      title 'Clinical Trial for Treatment of Migraine Headaches';
   run;