Psychometric Evaluation of a Treatment Acceptance Measure for Use in Patients Receiving Treatment via Subcutaneous Injection

Abstract

Background: Alirocumab, a proprotein convertase subtilisin/kexin type 9 inhibitor, significantly reduces low-density lipoprotein cholesterol, but requires subcutaneous injections rather than oral pills. To measure patients' acceptance of this treatment modality, a new patient-reported outcome, the Injection-Treatment Acceptance Questionnaire (I-TAQ), was developed.

Objectives: To psychometrically evaluate the I-TAQ with patients at high risk of cardiovascular events receiving alirocumab.

Methods: The 22-item, 5-domain I-TAQ was administered cross-sectionally to 151 patients enrolled in alirocumab clinical trials. Item response distributions, factor and multitrait analyses, interitem correlations, correlations with an existing measure of acceptance (convergent validity), and comparison of known-groups were performed to assess the I-TAQ's psychometric properties.

Results: Completion rates were high, with no patients missing more than two items and 91.4% missing no data. All items displayed high ceiling effects (>30%) because of high treatment acceptance. Factor analysis supported the a priori hypothesized item-domain structure with good fit indices (root mean square error approximation = 0.070; comparative fit index = 0.988) and high factor loadings. All items demonstrated item convergent validity (item-scale correlation ≥0.40), except for the side effects domain, which was limited by small numbers (n = 46). Almost all items correlated most highly with the domain to which they were assigned (item discriminant validity). Internal reliability was acceptable for all domains (Cronbach α range 0.72-0.88) and convergent validity was supported by a logical pattern of correlations with the Chronic Treatment Acceptance Questionnaire.

Conclusions: These findings provide initial evidence of validity and reliability for the I-TAQ in patients treated with subcutaneous alirocumab. The I-TAQ could prove to be a valuable patient-reported outcome for therapies requiring subcutaneous injection.

Keywords: acceptance; instrument development; patient-reported outcome; qualitative research.

Copyright © 2017 International Society for Pharmacoeconomics and Outcomes Research (ISPOR). Published by Elsevier Inc. All rights reserved.