The Adherence Scale in Chronic Diseases (ASCD). The power of knowledge: the key to successful patient — health care provider cooperation

Abstract

Introduction. Patients’ adherence to long-term therapies is low. It translates into reduced quality of life and significant deterioration of health economics. Identification of potential barriers of medication-related adherence is a starting point allowing implementation of more advanced interventions directed to adherence improvement.

Aim. The purpose of our study was to create and validate a simple instrument used to assess patients’ adherence to recommended medications.

Material and methods. The Adherence Scale in Chronic Diseases is a self-reported questionnaire with 8 items and with proposed 5 sets of answers. The total score in the Adherence Scale in Chronic Diseases ranges from 0 to 32 points. Three levels of adherence were considered (low: scores of 0 to 20; medium 21 to 25; high > 26). The validation of the questionnaire was conducted in accordance with the validation procedure. Assessment of the internal consistency was performed using a-Cronbach coefficient. In order to conduct the factor analysis, we assessed: the determinant of correlation matrix, Kaiser-Mayer-Olkin (K-M-O) statistic and the Bartlett’s test of sphericity. Factor analysis was conducted using principal component analysis with Oblimin rotation. The Kaiser criterion and scree plot were used in order to determine components of the questionnaire. Adherence levels were determined based on the percentiles.

Results. Grand total of 413 patients with a cardiovascular disease were included in the study. The reliability and homogeneity of the questionnaire were confirmed by a-Cronbach coefficient (0.739). Factor analysis showed that in this questionnaire we can extract two components. The analysis of factor loadings indicated excluding item 2 from the questionnaire. After exclusion of the mentioned item, we repeated the validation procedure. For such a new dataset, according to the Kaiser criterion, only one component was extracted.

Conclusions. The Adherence Scale in Chronic Diseases is a practical, reliable, consistent and well validated instrument for identifying specific obstacles to medication adherence. Its simplicity causes that it can be successfully applied in daily practice by health care professionals. Our survey has the potential to improve patient — health care professional communication and relationship.