The Adherence Estimator: a brief, proximal screener for patient propensity to adhere to prescription medications for chronic disease

Colleen A McHorney
Current Medical Research and Opinion 2009, 25 (1): 215-38

OBJECTIVE: To conceptualize, develop, and provide preliminary psychometric evidence for the Adherence Estimator--a brief, three-item proximal screener for the likelihood of non-adherence to prescription medications (medication non-fulfillment and non-persistence) for chronic disease.

RESEARCH DESIGN AND METHODS: Qualitative focus groups with 140 healthcare consumers and two internet-based surveys of adults with chronic disease, comprising a total of 1772 respondents, who were self-reported medication adherers, non-persisters, and non-fulfillers. Psychometric tests were performed on over 150 items assessing 14 patient beliefs and skills hypothesized to be related to medication non-adherence along a proximal-distal continuum. Psychometric tests included, but were not limited to, known-groups discriminant validity at the scale and item level. The psychometric analyses sought to identify: (1) the specific multi-item scales that best differentiated self-reported adherers from self-reported non-adherers (non-fulfillers and non-persisters) and, (2) the single best item within each prioritized multi-item scale that best differentiated self-reported adherers from self-reported non-adherers (non-fulfillers and non-persisters).

RESULTS: The two rounds of psychometric testing identified and cross-validated three proximal drivers of self-reported adherence: perceived concerns about medications, perceived need for medications, and perceived affordability of medications. One item from each domain was selected to include in the Adherence Estimator using a synthesis of psychometric results gleaned from classical and modern psychometric test theory. By simple summation of the weights assigned to the category responses of the three items, a total score is obtained that is immediately interpretable and completely transparent. Patients can be placed into one of three segments based on the total score--low, medium, and high risk for non-adherence. Sensitivity was 88%--of the non-adherers, 88% would be accurately classified as medium or high risk by the Adherence Estimator. The three risk groups differed on theoretically-relevant variables external to the Adherence Estimator in ways consistent with the hypothesized proximal-distal continuum of adherence drivers.

CONCLUSIONS: The three-item Adherence Estimator measures three proximal beliefs related to intentional non-adherence (medication non-fulfillment and non-persistence). Preliminary evidence of the validity of the Adherence Evidence supports its intended use to segment patients on their propensity to adhere to a newly-prescribed prescription medication. The Adherence Estimator is readily scored and is easily interpretable. Due to its brevity and transparency, it should prove to be practical for use in everyday clinical practice and in disease management for adherence quality improvement. Study limitations related to sample representation and self reports of chronic disease and adherence behaviors were discussed.

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