Reliability and convergent validity of two outcome instruments for pemphigus.
A major obstacle in performing multicenter controlled trials for pemphigus is the lack of a validated disease activity scoring system. Here, we assess the reliability and convergent validity of the PDAI (pemphigus disease area index). A group of 10 dermatologists scored 15 patients with pemphigus to estimate the inter- and intra-rater reliability of the PDAI and the recently described ABSIS (autoimmune bullous skin disorder intensity score) instrument. To assess convergent validity, these tools were also correlated with the Physician's Global Assessment (PGA). Reliability studies demonstrated an intra-class correlation coefficient (ICC) for inter-rater reliability of 0.76 (95% confirdence interval (CI)=0.61-0.91) for the PDAI and 0.77 (0.63-0.91) for the ABSIS. The tools differed most in reliability of assessing skin activity, with an ICC of 0.39 (0.17-0.60) for the ABSIS and 0.86 (0.76-0.95) for the PDAI. Intra-rater test-retest reliability demonstrated an ICC of 0.98 (0.96-1.0) for the PDAI and 0.80 (0.65-0.96) for the ABSIS. The PDAI also correlated more closely with the PGA. We conclude that the PDAI is more reproducible and correlates better with physician impression of extent. Subset analysis suggests that for this population of mild-to-moderate disease activity, the PDAI captures more variability in cutaneous disease than the ABSIS.
Rosenbach
Misha
M
Department of Dermatology, University of Pennsylvania, Philadelphia, PA 19119, USA.
Murrell
Dedee F
DF
Bystryn
Jean-Claude
JC
Dulay
Sam
S
Dick
Sarah
S
Fakharzadeh
Steve
S
Hall
Russell
R
Korman
Neil J
NJ
Lin
Julie
J
Okawa
Joyce
J
Pandya
Amit G
AG
Payne
Aimee S
AS
Rose
Mathew
M
Rubenstein
David
D
Woodley
David
D
Vittorio
Carmela
C
Werth
Benjamin B
BB
Williams
Erik A
EA
Taylor
Lynne
L
Troxel
Andrea B
AB
Werth
Victoria P
VP
D006801:Humans; D015588:Observer Variation; D017063:Outcome Assessment, Health Care / Q000592:standards*; D010147:Pain Measurement; D010392:Pemphigus / Q000145:classification* / Q000188:drug therapy / Q000473:pathology*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012720:Severity of Illness Index; D012867:Skin / Q000473:pathology