Inter-Rater Reliability And Agreement Of The Diagnostic Assessment Scale For Kushtha In Papulosquamous Skin Disease: A Cross-Sectional Two-Rater Study
TL;DR
DASK measures the severity of papulosquamous Kushtha reliably enough for group comparison and, against a threshold of 8 points, for individual monitoring.
Abstract
Background and objectives: The Diagnostic Assessment Scale for Kushtha (DASK) is a newly developed 26-item ordinal instrument that renders the classical threefold Ayurvedic examination as a severity score and a dosha attribution. No reliability estimate has been published. This study estimated its inter-rater reliability, agreement, and the measurement error attaching to an individual score. Methods: Sixty consecutive patients with consultant-confirmed papulosquamous disease (43 psoriasis, 17 lichen planus) were each assessed independently by two postgraduate-qualified Ayurvedic physicians in a single clinical session, giving a fully crossed design of 3,120 item scores. Reliability was estimated as the intraclass correlation coefficient ICC(2,1); agreement as the standard error of measurement (SEM), minimal detectable change (MDC95) and Bland–Altman limits; and item-level agreement as quadratic weighted kappa with Gwet’s AC2. Internal consistency and categorical agreement were also assessed, following the GRRAS guidelines. Results: No data were missing. ICC(2,1) was 0.952 (95% confidence interval 0.92–0.97) for the total score and 0.945, 0.920 and 0.920 for the Vata, Pitta and Kapha subscales. Between-patient variance accounted for 95.2% of total variance and the rater effect for 0.0–0.6%. SEM was 2.60 points and MDC95 7.21 points on the 0–104 scale, and all 26 items reached substantial or almost-perfect agreement (weighted kappa 0.732–0.963). The categorical outputs were less reliable than the scores generating them: severity band kappa 0.800 and dosha attribution kappa 0.640 (0.37–0.85), every disagreement occurring at a cut-point or a narrow margin. Kapha was reproduced consistently yet was not internally coherent (alpha 0.43 and 0.42). Conclusion: DASK measures the severity of papulosquamous Kushtha reliably enough for group comparison and, against a threshold of 8 points, for individual monitoring. Agreement on its categorical outputs was lower than on the continuous scores from which they are derived, and the Kapha subscale was reproduced consistently between raters without cohering internally.