I know what you mean... i've been trying to figure this out for over a month now. Turns out, it's way easier to do it in Stata, but my dataset is way to large for Stata to handle, so I've had to resort back to SAS. If your dataset is not very large, try running this in Stata. You have to install command twopm, and it's literally just few lines of code. Goodluck,
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