Disease activity score for children with juvenile dermatomyositis: reliability and validity evidence.
OBJECTIVE
To assess the reliability and validity of the Disease Activity Score (DAS), an instrument used to evaluate children with juvenile dermatomyositis (JDM).


METHODS
Psychometric study of internal consistency, reliability, rater agreement, and the relationship with measures of muscle strength and disability was conducted.


RESULTS
The DAS ratings are internally consistent (reliability = 0.89) and describe a wide range of disease activity. The pediatric rheumatologists in this study agree on the presence of most of the disease indicators. Their disagreements tend to cancel each other, resulting in highly correlated (r = 0.79) overall measures across raters. Estimates of muscle weakness using the DAS and ratings of muscle strength obtained independently from therapists are highly related (r = -0.77), but estimates of disease activity and disability are weakly related (r = 0.20).


CONCLUSIONS
The DAS exhibits evidence of good reliability and validity. The combination of skin and muscle strength assessments makes this easily administered instrument a useful addition in the evaluation of children with JDM.
Bode
Rita K
RK
Northwestern University Medical School, Chicago, Illinois, USA.
Klein-Gitelman
Marisa S
MS
Miller
Michael L
ML
Lechman
Toula S
TS
Pachman
Lauren M
LM
D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D003882:Dermatomyositis / Q000175:diagnosis* / Q000503:physiopathology*; D004185:Disability Evaluation; D005260:Female; D006801:Humans; D008297:Male; D009119:Muscle Contraction; D015588:Observer Variation; D011594:Psychometrics / Q000592:standards / Q000706:statistics & numerical data; D015203:Reproducibility of Results; D012720:Severity of Illness Index