The Coeliac Disease Assessment Questionnaire (CDAQ)
The Coeliac Disease Assessment Questionnaire (CDAQ) is a 32-item, patient-reported outcome measure developed to investigate the health-related quality of life of people living with coeliac disease.
The CDAQ was developed by researchers within the Health Services Research Unit, part of the Nuffield Department of Population Health at the University of Oxford. There are two existing disease-specific PROMs that assess quality of life in people with coeliac disease, the Celiac Disease Questionnaire (CDQ) and the Coeliac Disease Quality of Life Survey (CD-QOL). However, there are limitations in the development of both measures, including the derivation of items. The CDAQ has been developed according to current best practice guidelines. The measure can be used in a range of settings, including clinical trials and clinical practice.
Dimension scores and an overall index score can be calculated for the CDAQ. Raw scores are transformed to a 0-100 scale, where 0 is the poorest quality of life as measured by the CDAQ, and 100 is the highest quality of life as measured by the CDAQ. Details of the scoring system for the CDAQ can be downloaded in Dossier Extracts section.
An overview of the development process of The Coeliac Disease Assessment Questionnaire (CDAQ) is outlined below.
1. Derivation of items
Qualitative interviews were conducted with 23 adults with coeliac disease. Variation was sought across participant’s demographic and disease characteristics, particularly gender, age, and duration since diagnosis. Interview data was audio-recorded with the participant’s consent and transcribed verbatim. Interview data was analysed thematically in NVivo9. Following analysis, 63 candidate items were developed.
2. Refinement of items
Experts, including health professionals and researchers, provided feedback on candidate items via individual interviews and an expert panel. Revisions to items were made based on their comments. Following revisions, ten cognitive interviews were conducted with adults with coeliac disease across two rounds, with revisions to the questionnaire occurring after each round. Interviews examined cognitive thought processes during questionnaire completion in order to identify sources of response error.
Finally, a translatability assessment was undertaken to assess the cultural and linguistic translatability of the questionnaire.
3. Item reduction and scale generation
A draft 51-item version of the CDAQ was completed by 412 people with coeliac disease. Nineteen items were removed following data analysis. A principal components analysis (with Varimax rotation) was conducted on the remaining 32 items, identifying six meaningful dimensions, two of which were merged. Cronbach’s alpha values ranged between 0.82 and 0.88 for all dimensions, indicating good internal consistency.
4. Evaluation of psychometric properties
The CDAQ was completed by a further 268 people in order to evaluate the psychometric properties of the measure.
The final CDAQ contains 32 items addressing the five dimensions below. It measures health-related quality of life using a recall period of the past four weeks.
- stigma (8 items)
- dietary burden (8 items)
- symptoms (5 items)
- social isolation (5 items)
- worries and concerns (6 items).
A study to assess the CDAQ’s responsiveness to change is currently underway.