Factor structure and convergent validity of the Derriford Appearance Scale-24 using standard scoring versus treating not applicable' responses as missing data: A Scleroderma Patient-centered Intervention Network (SPIN) cohort study

Merz, Erin; Kwakkenbos, Linda; Carrier, Marie Eve; Gholizadeh, Shadi; Mills, Sarah D; Fox, Rina S; Jewett, Lisa R; Williamson, Heidi; Harcourt, Diana; Assassi, Shervin; Furst, Daniel; Gottesman, Karen; Mayes, Maureen D; Moss, Tim; Thombs, Ryan; Malcarne, Vanessa L.

Abstract

© 2018 Article author(s) (or their employer(s) unless otherwise stated in the text of the article). All rights reserved. Objective Valid measures of appearance concern are needed in systemic sclerosis (SSc), a rare, disfiguring autoimmune disease. The Derriford Appearance Scale-24 (DAS-24) assesses appearance-related distress related to visible differences. There is uncertainty regarding its factor structure, possibly due to its scoring method. Design Cross-sectional survey. Setting Participants with SSc were recruited from 27 centres in Canada, the USA and the UK. Participants who self-identified as having visible differences were recruited from community and clinical settings in the UK. Participants Two samples were analysed (n=950 participants with SSc; n=1265 participants with visible differences). Primary and secondary outcome measures The DAS-24 factor structure was evaluated using two scoring methods. Convergent validity was evaluated with measures of social interaction anxiety, depression, fear of negative evaluation, social discomfort and dissatisfaction with appearance. Results When items marked by respondents as not applicable' were scored as 0, per standard DAS-24 scoring, a one-factor model fit poorly; when treated as missing data, the one-factor model fit well. Convergent validity analyses revealed strong correlations that were similar across scoring methods. Conclusions Treating not applicable' responses as missing improved the measurement model, but did not substantively influence practical inferences that can be drawn from DAS-24 scores. Indications of item redundancy and poorly performing items suggest that the DAS-24 could be improved and potentially shortened.

• Journal Article Type: Article
• Acceptance Date: Jan 18, 2018
• Publication Date: Mar 1, 2018
• Deposit Date: Feb 6, 2018
• Publicly Available Date: Mar 26, 2018
• Journal: BMJ Open
• Electronic ISSN: 2044-6055
• Publisher: BMJ Publishing Group
• Peer Reviewed: Peer Reviewed
• Volume: 8
• Issue: 3
• Pages: 1-9
• DOI: https://doi.org/10.1136/bmjopen-2017-018641
• Keywords: visible difference
• Public URL: https://uwe-repository.worktribe.com/output/875140
• Publisher URL: http://dx.doi.org/10.1136/bmjopen-2017-018641
• Contract Date: Feb 6, 2018