Hi all, I would like to exam effect of two kinds of treatment (A, B) on health outcome (death vs non), stratified by a third variable (level 1, level 2, level 3). The problem is that % by level in treatment A is so different from that in B. For example: 89% level 1, 5% level 2, and 6% level 3 in treatment A, while 35% level 1, 50% level 2, and 15% level 3 in treatment B. If I conduct the analyses among level 1 group, meaning 89% of the treatment A and only 35% of the treatment B. Do you think this may cause any bias? if so, can you please share some references about it? Thanks!
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