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. 2018 Mar 6;8(3):e018641. doi: 10.1136/bmjopen-2017-018641.


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.

Keywords: Das-24; confirmatory factor analysis; derriford appearance scale; psychometrics; systemic sclerosis.

Publication types

  • Comparative Study
  • Evaluation Study
  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Validation Study

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Aged, 80 and over
  • Body Image*
  • Canada
  • Cohort Studies
  • Cross-Sectional Studies
  • Female
  • Humans
  • Male
  • Middle Aged
  • Physical Appearance, Body*
  • Psychometrics
  • Reproducibility of Results
  • Research Design / standards*
  • Scleroderma, Systemic / psychology*
  • Stress, Psychological / etiology*
  • Surveys and Questionnaires / standards*
  • United Kingdom
  • United States
  • Young Adult