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Causal diagram depicting assessment of the effect of bisphosphonate (X) on radiographic osteoarthritis (ROA) progression (Y) and their relationship with mediators of baseline ROA (M0) and bone marrow lesions (BMLs; M1) as well as other unspecified mechanisms. Here the study design involves conditioning upon M0 by restricting the study sample to those with a specific value of M0 (box); the same issues arise when variable M0 is simply adjusted for in the analyses.
