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Quality of Life Research
Published in: Quality of Life Research 1/2012

Open Access 01-02-2012

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

Authors: 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

Published in: Quality of Life Research | Issue 1/2012

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Abstract

Purpose

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.

Methods

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.

Results

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 unexplained variance by the first contrast of both scales was 1.7 units. Spearman correlation between the Observer Scale Rasch measure and the overall opinion of the clinician was 0.75.

Conclusion

The Rasch model demonstrated that the POSAS is a reliable and valid scale that measures the single-construct scar quality.
Appendix
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Metadata
Title
Rasch analysis of the Patient and Observer Scar Assessment Scale (POSAS) in burn scars
Authors
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
Publication date
01-02-2012
Publisher
Springer Netherlands
Published in
Quality of Life Research / Issue 1/2012
Print ISSN: 0962-9343
Electronic ISSN: 1573-2649
DOI
https://doi.org/10.1007/s11136-011-9924-5

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