From a sample of 1000 patients, the number who take a certain drug within 6 months BEFORE a heart attack is 400, and the number who take that drug within 6 months AFTER a heart attack is 550. What SAS test can I run to determine if the BEFORE and AFTER numbers are significantly different? Note that some patients may be in both groups. thanks.
As shown in the output stat, the p-value (<.0001) suggests that the two groups (before and after) are not independent. Look into the Risk Estimates table, there is significant difference between the group proportions.