Original ArticleComparison of two self-rating instruments for medication adherence assessment in hypertension revealed insufficient psychometric properties
Introduction
If evidence-based and effective therapies do not show the desired effect, a lack of patient medication adherence is often considered the main reason for this failure. In the case of hypertensive patients, a considerable proportion thereof has insufficient blood pressure control [1], and many authors suggest that a frequent reason is low medication adherence [2].
In clinical research, medical event monitoring systems that electronically record every opening of a pill box and similar methods are regarded as the current “gold standard” for adherence assessment [3], [4]. However, their use in clinical practice is limited by at least two reasons: (1) high cost and (2) an atmosphere of control that might be counterproductive to the role of the patient as an active and autonomous agent in health-care decisions [5]. With respect to the patient perspective, the definition and degree of medication adherence should be a matter of “patient decision making” [6] or “asserting control over one's disorder” [7]. For practitioners, who must distinguish between “nonadherence” and “nonresponse” to antihypertensive treatment in daily practice [8], a short and valid adherence measurement based on the patient's self-report may be helpful.
The two scales frequently used in medication adherence research for hypertension are the “Hill-Bone Compliance to High Blood Pressure Therapy Scale” (Hill-Bone Scale) [9] and the “Self-Reported Measure of Medication Adherence” (Morisky-Green Scale) [10]. These instruments seem to be appropriate not only in treatment studies but also to inform practitioners and facilitate a frank discussion with the patient about his or her medication adherence. Both scales are short and easy to answer. The validity and reliability of these instruments have been investigated in some earlier studies [10], [11] but not with homogenous results. Moreover, to our knowledge both adherence scales have not been compared in the same study population.
The aim of our study was to test the acceptability, reliability, and validity of the Hill-Bone Scale and the Morisky-Green Scale. In particular, we assessed the convergent validity of both instruments and the criterion validity, that is, the strength of association between the scales and the quality of blood pressure control as reported by the patients themselves.
Section snippets
Study design and data collection procedures
This study was part of the MedViP project (“Medizinische Versorgung in der Praxis”—Medical Care in General Practice). The study protocol was approved by the University of Göttingen Research Ethics Committee. The design and recruitment have been described in detail elsewhere [12]. In brief, general practitioners were invited to provide routinely collected electronic medical data. Electronic patient records were extracted via a standardized interface.
We identified pseudonymized patient codes with
Results
The statistical analyses of the psychometric properties of the two medication adherence scales were based on 353 patients (from 23 general practices) who received drug treatment for their arterial hypertension. Table 1 provides a detailed description of the study sample.
Discussion
On the basis of a sample of 353 patients with drug-treated hypertension, we examined the psychometric properties of two self-rating instruments for medication adherence, the “Hill-Bone Compliance to High Blood Pressure Therapy Scale” [9] and the “Self-Reported Measure of Medication Adherence” [10]. Both instruments showed an insufficient psychometric quality in different aspects of acceptability, reliability, and validity.
Acknowledgments
We thank all patients who participated in this study for their cooperation. The assistance of Hannelore Schneider-Ruth in collecting the data is gratefully acknowledged.
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