Interpretation and precision of the Observer Scar Assessment Scale improved by a revised scoring.

Objective: To apply Rasch measurement to develop a rule for clinical interpretation of the Observer Scar Assessment Scale (OSAS) to help surgeons judge reported sum scores clinically.

Study Design And Setting: We used cross-sectional data of a multicenter randomized clinical trial for the treatment of nontuberculous cervicofacial lymphadenitis in children. Rasch analysis was used on the OSAS scores obtained from scar photographs of 100 children after surgical or antibiotic treatment.

Results: Rasch analysis showed that all OSAS item rating scales needed revision and weighting. After doing so, raw scale scores could be converted into quantitative interval scale-based measures of scar quality. The clinical interpretation of the OSAS was clearly improved by the revised scoring. By using the Rasch-modeled item and person measures, the most likely OSAS score patterns associated with the revised OSAS sum scores could be determined.

Conclusions: The Rasch analysis improved the measurement properties and clinical interpretability of the OSAS instrument.