Purpose: The treatment for coeliac disease (CD) is a gluten-free diet (GFD), which impacts the health-related quality of life (HRQoL). The aim of the study was to develop the Gluten-Free Diet Perceived Competence Scale (GFD-PCS): a short and precise CD-specific patient-reported outcome measure.Methods: The GFD-PCS was developed from the scales 'Perceived Competence (Maintaining a Healthy Diet)' and 'Perceived Competence for Diabetes'. The scale was then programmed into a web-based questionnaire and distributed together with generic quality of life (WHO-5) and CD-specific HRQoL (CDQL) questionnaires.Results: There were 931 respondents. The 831 who reported 'diagnosed CD' were retained. The average age was 37.6 years (SD = 16.5). There was no statistically significant difference between males (M = 5.9, SD = 1.6) and females (M = 6.2, SD = 1.4) in GFD-PCS score. Respondents younger than 18 years (n = 104) scored lower (M = 5.8, SD = 1.4) than adults (M = 6.2, SD = 1.4). The psychometric properties of the GFD-PCS showed excellent internal reliability (α = .96) and satisfied construct and criterion validity.Conclusion: The GFD-PCS measures patient-perceived dietary competence for maintaining a GFD. The scale is psychometrically robust and provides a useful tool in assessing patients' difficulties with a GFD.
Keywords: Coeliac disease; gluten-free diet; perceived competence; quality of life; scale development.