Objective: To present common language for defining adherence of infrequent yet repeated health behaviors.
Methods: We illustrate methodological and conceptual issues using human papillomavirus (HPV) vaccination and screening mammography study data as examples.
Results: Adherence rates of infrequent, repeated behaviors varied widely depending on how adherence was defined and measured. We advocate use of 3 standard definitions of adherence: initiation of behavior (initiation), adherence to most recent opportunity (on-schedule), and timely adherence across multiple opportunities (maintenance or completion).
Conclusions: The proposed framework has cross-cutting implications for research and practice. Standardizing adherence metrics may facilitate comparisons across studies of health behaviors practiced at infrequent yet repeated intervals.