Abstract
BackgroundTaking DMARDs as prescribed is an essential part of self-management for patients with Rheumatoid Arthritis. To date, the Compliance Questionnaire for Rheumatology (CQR) is the only self-report adherence measure created specifically for and validated in rheumatic diseases. However, the factor structure of the CQR has not been reported and it can be considered lengthy at 19 items. The aim of this study was to test the factor structure of the CQR and reduce the number of items whilst retaining robust explanation of non-adherence to DMARDs. Such a reduction would increase the clinical utility of the scale, to identify patients with sub-optimal adherence to DMARDs in the clinic as well as for research purposes.MethodsAn exploratory factor analysis was performed to reduce the number of items in the CQR and then a confirmatory factor analysis was run to establish the fit of a 5 item version (CQR5) to the data. A discriminant function analysis was performed to determine the optimal combination of questions to identify suboptimal adherence.ResultsThe factor analyses identified a unidimensional 5 item model that explains 50.3% of the variance in adherence and has good internal consistency and fit to the data. Discriminant function analysis shows that the CQR5 can affectively detect 69% of low adherers to DMARDs using Fisher’s weighted regression equation.ConclusionA shortened version of the CQR increases the clinical utility by reducing the patient burden whilst maintaining a good level of reliability and validity for a short, self-administered, self-report questionnaire.
Highlights
Taking DMARDs as prescribed is an essential part of self-management for patients with Rheumatoid Arthritis
Exploratory factor analysis of CQR19 The initial EFA of the CQR19 showed 6 eigen-values >1 which accounted for 61.6% of the variance in adherence, which is somewhat higher than the original authors found at 46% [12]
The Kaiser-Meyer-Olkin Measure of Sampling Adequacy (KMO) = 0.79 which indicates a weak factor structure [20]. This can be seen as the eigen-values of two of the factors were very low at 1.09 and 1.04, a trait which is enhanced by the fact that the factor matrix indicated that only one item loaded highly on each of factors 2–6 suggesting that the additional factors were the product of items that inadequately measure medication adherence
Summary
Taking DMARDs as prescribed is an essential part of self-management for patients with Rheumatoid Arthritis. The Compliance Questionnaire for Rheumatology (CQR) is the only self-report adherence measure created for and validated in rheumatic diseases. The extent to which a patient takes medication as prescribed is termed “adherence” [5]. A patient who is fully adherent never (or rarely) misses or changes doses of the prescribed medication. Medication non-adherence in various chronic illnesses is typically quoted at 30-50% [9,10]; non-adherence rates for DMARDs in RA are often higher at 41% [11] and up to 75% for correct dosing [2,12]
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