For some reason, when I edit the dataset i get it correct but it is not when posted. Here are the correct entries: id rx
1 a
1 b
1 d
2 a
2 b
3 a
3 c
4 b 5 a 5 d 6 a 6 c 7 a 7 b for patient 4 (b), patient 5 (a, d), patient 6 (a, c) and patients 7 (a,b) so you get 2 for a-c because patient 3 had a-c and patient 6 has a-c too. You are right for a-d, the triple combination can be counted under different category so for patient 1, it could be a-b, a-d and b-d and a-b-d but for smipliciy, I would count this only once as a-b-c so patient can be counted only one time in the aggregate measure.
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