![Counting observations for which two events occur](https://blogs.sas.com/content/iml/files/2016/10/pairwise3.png)
Every year near Halloween I write an article in which I demonstrate a simple programming trick that is a real treat to use. This year's trick (which features the CMISS function and the crossproducts matrix in SAS/IML) enables you to count the number of observations that are missing for pairs