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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.

Authors

Erin Merz

Linda Kwakkenbos

Marie Eve Carrier

Shadi Gholizadeh

Sarah D Mills

Rina S Fox

Lisa R Jewett

Heidi Williamson Heidi3.Williamson@uwe.ac.uk
Associate Professor in Applied Health Research

Shervin Assassi

Daniel Furst

Karen Gottesman

Maureen D Mayes

Ryan Thombs

Vanessa L. Malcarne



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.

Citation

Merz, E., Kwakkenbos, L., Carrier, M. E., Gholizadeh, S., Mills, S. D., Fox, R. S., …Malcarne, V. L. (2018). 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. BMJ Open, 8(3), 1-9. https://doi.org/10.1136/bmjopen-2017-018641

Journal Article Type Article
Acceptance Date Jan 18, 2018
Publication Date Mar 1, 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

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