LAUSR

AIM To assess heterogeneity in adherence to medications in two example comparative effectiveness research studies. PATIENTS & METHODS We analyzed data from commercially insured patients initiating a statin or anticoagulant during 2005-2012. We calculated the cross-validated R2 from a series of hierarchical linear models to assess variation in 1-year adherence. RESULTS There was less heterogeneity in adherence in the statin cohort compared with the anticoagulant cohort, where patient characteristics explained 7.2% of variation in adherence, and adding therapy and provider characteristics increased the proportion of variation explained to 8.0 and 8.5%, cumulatively. Random effects provided essentially no explanatory power, even in the statin cohort with large numbers of patients clustered within each pharmacy, prescriber and provider. CONCLUSION The dependence of adherence on the healthcare system was stronger when the healthcare system influenced treatment choice and patient access to medication and when indications for treatment were strong.