Measuring pharmacy performance in the area of medication adherence: addressing the issue of risk adjustment

Pharmacies and pharmacists play an important role in the health care system, improving health outcomes and enhancing quality through better pharmaceutical care. Yet, little information is available to accurately evaluate pharmacy store quality and thereby encourage quality improvement at the pharmacy store level.

To (a) assess pharmacy performance in the area of medication adherence and (b) examine the impact of risk adjustment of performance scores on pharmacy rankings.

We used proportion of days covered (PDC) to compute pharmacy performance scores using the 2007 Mississippi Medicare administrative claims dataset. We calculated unadjusted and adjusted quality scores for 685 pharmacies serving 137,497 eligible Medicare beneficiaries. Risk-adjusted quality scores were computed using a hierarchical logistic regression model (Method 1) and the shrinkage estimators of the model (Method 2). Patient demographics, income subsidy status, and comorbidity burden were used as variables for risk adjustment.

Unadjusted scores showed low levels of agreement (Cohen's kappa  less than  0.45) with risk-adjusted scores in identifying statistical outliers based on 95% CIs. Unadjusted scores also failed to identify 39%-43% of the top 20% and bottom 20% of pharmacies and displayed moderate agreement (0.4  less than  kappa  less than  0.5) with risk-adjusted scores. Pharmacy classifications based on risk-adjusted scores obtained from different statistical methods showed high levels of agreement (0.79  less than  kappa  less than  0.98).

In the risk-adjustment methods presented here, we account for many patient characteristics previously reported to be associated with medication adherence and available in our dataset. Risk-adjusted scores produced more robust indicators of pharmacy quality than unadjusted scores. Depending on the availability of important variables in the source data, the use of risk-adjusted quality indicators may lead to better evaluation of pharmacy quality and should be considered when providing public reports on pharmacy quality.