Variation in adherence to medications across the healthcare system in two comparative effectiveness research cohorts.

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 R(2) 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.