Event  
Group Occurred (Y=1) Not occurred (Y=0) Total
Treatment (X=1) n11,1+n10,1 n00,1+n01,1 n11,1+n10,1+n01,1+n00,1
Control (X=0) n11,0+n01,0 n00,0+n10,0 n11,0+n10,0+n01,0+n00,0
Total n11+n10,1+n01,0 n00+n01,1+n10,0 n
Table 3: Two-by-two contingency table with the numbers for the four types of subjects defining the four principal strata.