Development and Psychometric Evaluation of the Peritoneal Dialysis Treatment Adherence Scale: A Multicenter Methodological Study

Background/Objectives: Peritoneal dialysis (PD) requires patients to manage dialysis procedures, medications, fluid intake, and nutrition at home. Existing assessment approaches do not adequately distinguish patients’ treatment-related knowledge and awareness from their self-reported adherence practices across these domains. This study aimed to develop and psychometrically evaluate the Peritoneal Dialysis Treatment Adherence Scale, a patient-reported instrument designed to assess treatment-related knowledge/awareness and self-reported adherence practices in peritoneal dialysis. Methods: This multicenter methodological study included 600 adults receiving PD at eight hospitals in Türkiye. An initial 64-item pool was evaluated by 12 experts and pilot-tested with 30 patients. The main sample was randomly divided into two independent subsamples of 300 participants for exploratory factor analysis (EFA) and confirmatory factor analysis (CFA). EFA was conducted using principal axis factoring with direct oblimin rotation, and Horn’s parallel analysis was used to determine factor retention. CFA was conducted in the independent confirmatory subsample. Internal consistency was evaluated using Cronbach’s alpha and McDonald’s omega, and three-week test–retest reliability was assessed in 30 participants using intraclass correlation coefficients. Results: The final instrument comprised a 32-item Knowledge Dimension, assessing self-reported treatment knowledge and awareness, and a 25-item Adherence Practices Dimension, assessing the frequency and consistency of self-reported adherence practices. Primary factor loadings ranged from 0.694 to 0.971 for Knowledge and from 0.508 to 0.951 for Adherence Practices, with no items meeting the prespecified criterion for problematic cross-loading. Separate four-factor CFA models demonstrated acceptable within-dimension fit; however, the additional integrated eight-factor CFA including all 57 items did not meet all conventional global-fit criteria, indicating that the overall measurement structure requires further independent validation. Internal consistency in the independent confirmatory subsample was high for both dimensions: Knowledge, α = 0.950 and ω = 0.984; Adherence Practices, α = 0.952 and ω = 0.986. Test–retest reliability was strong for Knowledge (ICC = 0.946) and Adherence Practices (ICC = 0.940). Conclusions: The Peritoneal Dialysis Treatment Adherence Scale demonstrated promising but provisional structural evidence, high internal consistency, and strong temporal stability. Its separately scored Knowledge and Adherence Practices dimensions may support domain-specific assessment in PD; however, the overall eight-factor measurement structure requires further independent validation before widespread clinical use.