Studying the use of oral contraception: a review of measurement approaches

BACKGROUND: Although oral contraception (OC) misuse is presumed to play an important role in unwanted pregnancy, research findings have often been equivocal, perhaps reflecting unaddressed inconsistencies in methodological approaches. METHODS: Using established databases, we performed a systematic review of measurement methods for OC use using primary research reports published from January 1965 to December 2009. RESULTS: Terminology used to describe OC use, which included continuation, compliance, and adherence, differed across studies and was rarely defined. The majority of studies (n = 27 of 38, 71%) relied solely on self-report measures of OC use. Only two reports described survey or interview questions, and reliability and validity data were seldom described. More rigorous measurement methods, such as pill counts (electronic or manual), serum and urinary biomarkers, and pharmacy records, were infrequently employed. Nineteen studies simultaneously used more than one method, but only three studies compared direct and indirect methods. CONCLUSIONS: The lack of a consistent, well-defined measurement of OC use limits our understanding of contraceptive misuse and related negative outcomes. Future research should clarify terminology, develop standardized measures, incorporate multimethod approaches with innovative methods, and publish details of measurement methods