Psychometric Properties of the COPD-Specific Beliefs About Medicine Questionnaire in an Outpatient Population: A Rasch-Analysis

Abstract

Background: Understanding non-adherence in patients with chronic obstructive pulmonary disease (COPD) remains challenging. The necessity and the concerns scales of the Beliefs about Medicines Questionnaire (BMQ) are known to correlate with adherence behavior in several chronic diseases including asthma but less is known about COPD. In the present study a COPD-specific BMQ (BMQ-COPD) was translated and administered to Danish COPD outpatients. Our aim was to derive high-quality measures of the 2 dimensions included in the BMQ-COPD. Methods: A total of 168 patients with COPD were included from a Danish respiratory outpatient clinic. The Rasch model was used to evaluate psychometric characteristics of the BMQ-COPD and to obtain necessity and concerns scales fulfilling criteria of unidimensionality and overall fit, and with all items showing individual item fit with no local dependencies, and no differential item functioning. Further, we explored the association with disease-related variables and subsequent adherence behavior. Results: Shortened versions of the original necessity and concerns scales fitted the Rasch model and were at least as good as the original scales as predictors of adherence, although only the necessity scale was significantly associated with adherence. Conclusion: In a Danish COPD setting high-quality measures of necessity and concerns could be derived from the BMQ-COPD. The excluded items appear to reflect other dimensions.