extended · article · 2011

Rasch analysis of the Patient and Observer Scar Assessment Scale (POSAS) in burn scars

Martijn B. A. van der Wal; Wim E. Tuinebreijer; Monica C. T. Bloemen; Pauline D. H. M. Verhaegen; Esther Middelkoop; Paul P. M. van Zuijlen

The Patient and Observer Scar Assessment Scale (POSAS) is a questionnaire that was developed to assess scar quality. It consists of two separate six-item scales (Observer Scale and Patient Scale), both of which are scored on a 10-point rating scale. After many years of experience with this scale in burn scar assessment, it is appropriate to examine its psychometric properties using Rasch analysis. Cross-sectional data collection from seven clinical trials resulted in a data set of 1,629 observer scores and 1,427 patient scores of burn scars. We examined the person–item map, item fit statistics, reliability, response category ordering, and dimensionality of the POSAS. The POSAS showed an adequate fit to the Rasch model, except for the item surface area. Person reliability of the Observer Scale and Patient Scale was 0.82 and 0.77, respectively. Dimensionality analysis revealed that the une...