Measuring oral contraceptive adherence using self-report versus pharmacy claims data

Objective Proportion of Days Covered (PDC) is a measure of medication adherence that uses prescription claims data to describe the proportion of days that the patient possessed medication. The objective of this study is to compare PDC and self-report as measures of oral contraceptive pills (OCPs) adherence and to identify individual-level predictors of adherence. Study design In a sample of 384 OCP users, self-report was compared with PDC as measures of adherence over the past 3 months. Patient-level variables were examined for associations with adherence using multivariable logistic regression models. Results High adherence, defined as missing ≤1 pill per month, was 76%, 68% and 54% as measured by self-report, PDC and both measures, respectively. Younger women (ages 18–25 and 26–33 years) were significantly less likely to have high adherence on both measures than women in the 34–40 age group [adjusted odds ratio (OR) 0.20, 95% confidence interval (CI) 0.08–0.51 and adjusted OR 0.26, 95% CI 0.11–0.62, respectively). Other predictors of high adherence on both self-report and PDC measures included being in a relationship (adjusted OR 2.30, 95% CI 1.14–4.64, compared with unpartnered women), Protestant religion (adjusted OR 2.08, 95% CI 1.07–4.06, compared with women with no religious affiliation) and higher contraceptive self-efficacy (adjusted OR 1.63, 95% CI 1.03–2.58). Conclusion PDC derived from pharmacy claims, or a combination of PDC and self-report measures, may be an alternative to self-report alone for measuring OCP adherence. Implications PDC may be a potential tool for measuring women's adherence to OCPs and should be validated in future studies.