Development and validation of treatment adherence questionnaire based on the theory of planned behaviour for...

To develop and validate a comprehensive treatment adherence questionnaire grounded in the theory of planned behaviour (TPB) for patients with end-stage renal disease (ESRD) undergoing haemodialysis in Pakistan.

An exploratory sequential mixed-method design was employed, comprising qualitative item generation followed by quantitative scale validation.

Phase 1 involved qualitative exploration for item development through an extensive literature review and four focus group discussions. An initial pool of 130 items was generated, which was refined through expert evaluation and redundancy removal, resulting in 87 Likert-type items. Phase 2 consisted of exploratory factor analysis (EFA) conducted on data from 350 purposively recruited ESRD patients to identify the underlying factor structure. In Study 2, confirmatory factor analysis (CFA) was performed on an independent sample of 300 patients to confirm the model and evaluate psychometric properties.

EFA revealed four adherence domains: medication, fluid, diet and haemodialysis, aligned with TPB components including attitude, subjective norms, perceived behavioural control and intentions. CFA demonstrated good model fit indices, and all items showed strong factor loadings, supporting structural validity. Internal consistency was satisfactory with Cronbach's alpha values above .70. Convergent validity was confirmed with average variance extracted values above .50, while discriminant validity was supported as AVE exceeded maximum shared variance.

The TPB-based treatment adherence questionnaire for ESRD is a reliable and valid instrument for assessing adherence behaviours among haemodialysis patients. It offers a theory-driven tool with strong potential for research and clinical interventions aimed at improving treatment adherence.