Methodological issues in adherence to cancer control regimens.

A six-factor model provides a heuristic framework for understanding adherence behavior: (1) effective provider communication; (2) rapport with provider; (3) client's beliefs and attitudes; (4) client's social climate and norms; (5) behavioral intentions; and (6) supports for and barriers to adherence. Four classes of methodological issues are discussed. Recruitment may be affected by the sociodemographics of the target population, biomedical variables, population size and location, and patient sources utilized. Interventions can be structured to maximize enrollment, participation and long-term retention, and adherence to the regimen promoted with behavioral methodology. Measurement of adherence optimally includes multiple measures at multiple time points, a well-defined focus and unit of adherence, well-constructed response options, and multiple sources of information. Sample size calculations and interpretation of clinical trial results are affected by adherence rates. Multivariate analytic techniques, such as structural equation modeling, make it possible to specify models depicting hypothesized structural relationships between different theoretical constructs and to evaluate the plausibility of these models.