RT Journal Article
SR Electronic
T1 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
JF BMJ Open
JO BMJ Open
FD British Medical Journal Publishing Group
SP e018641
DO 10.1136/bmjopen-2017-018641
VO 8
IS 3
A1 Erin L Merz
A1 Linda Kwakkenbos
A1 Marie-Eve Carrier
A1 Shadi Gholizadeh
A1 Sarah D Mills
A1 Rina S Fox
A1 Lisa R Jewett
A1 Heidi Williamson
A1 Diana Harcourt
A1 Shervin Assassi
A1 Daniel E Furst
A1 Karen Gottesman
A1 Maureen D Mayes
A1 Tim P Moss
A1 Brett D Thombs
A1 Vanessa L Malcarne
A1 ,
YR 2018
UL http://bmjopen.bmj.com/content/8/3/e018641.abstract
AB 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.