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, 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

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.

Figures

Fig. 1
Fig. 1
Person (n = 1,629) and item (6 items) or Wright map for the Observer Scale. Positive scores indicate poorer scar quality, whereas negative scores demonstrate better scar quality. Items from the scale are shown on the right-hand side of the figure, and person measures are highlighted by a ‘#’ or ‘.’ Each ‘#’ represents 24 subjects, and each ‘.’ represents 1–23. M mean, S 1 SD from the mean, T 2 SD from the mean
Fig. 2
Fig. 2
Person (n = 1,427) and item (6 items) or Wright map for the Patient Scale. Positive scores indicate poorer scar quality, whereas negative scores demonstrate better scar quality. Items from the scale are shown on the right-hand side of the figure, and person measures are highlighted by a ‘#’ or ‘.’ Each ‘#’ represents 13 subjects, and each ‘.’ represents 1–12. M mean, S 1 SD from the mean, T 2 SD from the mean
Fig. 3
Fig. 3
Category probability curve of the Observer Scale showing the probability of assigning to any particular category (y-axis), given the difference in estimates between any patient scar quality and any item difficulty. The threshold estimates correspond to the intersection of rating scale categories
Fig. 4
Fig. 4
Category probability curve of the Patient Scale with ten categories
Fig. 5
Fig. 5
Category probability curve of the refined Patient Scale with five categories

References

    1. Van Loey NE, Van Son MJ. Psychopathology and psychological problems in patients with burn scars: Epidemiology and management. American Journal of Clinical Dermatology. 2003;4:245–272. doi: 10.2165/00128071-200304040-00004.
    1. Falder S, Browne A, Edgar D, et al. Core outcomes for adult burn survivors: A clinical overview. Burns. 2009;35:618–641. doi: 10.1016/j.burns.2008.09.002.
    1. van Baar ME, Essink-Bot ML, Oen IM, Dokter J, Boxma H, van Beeck EF. Functional outcome after burns: A review. Burns. 2006;32:1–9. doi: 10.1016/j.burns.2005.08.007.
    1. van Zuijlen PP, Angeles AP, Kreis RW, Bos KE, Middelkoop E. Scar assessment tools: Implications for current research. Plastic and Reconstructive Surgery. 2002;109:1108–1122. doi: 10.1097/00006534-200203000-00052.
    1. Brusselaers, N., Pirayesh, A., Hoeksema, H., Verbelen, J., Blot, S., & Monstrey, S. (2010). Burn scar assessment: A systematic review of objective scar assessment tools. Burns, 36, 1157–1164.
    1. Nguyen DQ, Potokar T, Price P. A review of current objective and subjective scar assessment tools. Journal of Wound Care. 2008;17(101–102):104–106.
    1. Idriss N, Maibach HI. Scar assessment scales: A dermatologic overview. Skin Research Technology. 2009;15:1–5. doi: 10.1111/j.1600-0846.2008.00327.x.
    1. Durani P, McGrouther DA, Ferguson MW. Current scales for assessing human scarring: A review. Journal of Plastic, Reconstructive & Aesthetic Surgery. 2009;62:713–720. doi: 10.1016/j.bjps.2009.01.080.
    1. Draaijers, L. J., Tempelman, F. R., Botman, Y. A, et al. (2004). The patient and observer scar assessment scale: A reliable and feasible tool for scar evaluation. Plast Reconstr Surg, 113, 1960–1965 (discussion 1966–1967).
    1. van de Kar AL, Corion LU, Smeulders MJ, Draaijers LJ, van der Horst CM, van Zuijlen PP. Reliable and feasible evaluation of linear scars by the patient and observer scar assessment scale. Journal of Plastic, Reconstructive & Aesthetic Surgery. 2005;116:514–522.
    1. Truong PT, Lee JC, Soer B, Gaul CA, Olivotto IA. Reliability and validity testing of the patient and Observer Scar Assessment Scale in evaluating linear scars after breast cancer surgery. Plastic and Reconstructive Surgery. 2007;119:487–494. doi: 10.1097/01.prs.0000252949.77525.bc.
    1. O’Connell, D. A., Diamond, C., Seikaly, H., & Harris, J. R. (2008). Objective and subjective scar aesthetics in minimal access vs conventional access parathyroidectomy and thyroidectomy surgical procedures: A paired cohort study. Archives of otolaryngology–head & neck surgery, 134, 85–93.
    1. Sardesai MG, Moore CC. Quantitative and qualitative dermal change with microfat grafting of facial scars. Otolaryngology Head and Neck Surgery. 2007;137:868–872. doi: 10.1016/j.otohns.2007.08.008.
    1. Zaal LH, van der Horst CM. Results of the early use of tissue expansion for giant congenital melanocytic naevi on the scalp and face. Journal of Plastic, Reconstructive & Aesthetic Surgery. 2009;62:216–220. doi: 10.1016/j.bjps.2007.10.045.
    1. Cromi, A., Ghezzi, F., Gottardi, A., Cherubino, M., Uccella, S., & Valdatta, L. (2010). Cosmetic outcomes of various skin closure methods following cesarean delivery: A randomized trial. American Journal of Obstetrics and Gynecology, 203, 36 e31–36 e38.
    1. Kaartinen, I. S., Valisuo, P. O., Alander, J. T., & Kuokkanen, H. O. (2010). Objective scar assessment-A new method using standardized digital imaging and spectral modelling. Burns.
    1. Bianchi FA, Roccia F, Fiorini P, Berrone S. Use of patient and Observer Scar Assessment Scale for evaluation of facial scars treated with self-drying silicone gel. The Journal of Craniofacial Surgery. 2010;21:719–723. doi: 10.1097/SCS.0b013e3181d841af.
    1. Aust MC, Fernandes D, Kolokythas P, Kaplan HM, Vogt PM. Percutaneous collagen induction therapy: An alternative treatment for scars, wrinkles, and skin laxity. Plastic and Reconstructive Surgery. 2008;121:1421–1429. doi: 10.1097/01.prs.0000304612.72899.02.
    1. van der Wal MB, van Zuijlen PP, van de Ven P, Middelkoop E. Topical silicone gel versus placebo in promoting the maturation of burn scars: A randomized controlled trial. Plastic and Reconstructive Surgery. 2010;126:524–531. doi: 10.1097/PRS.0b013e3181e09559.
    1. Roques C, Teot L. A critical analysis of measurements used to assess and manage scars. The International Journal of Lower Extremity Wounds. 2007;6:249–253. doi: 10.1177/1534734607308249.
    1. Franchignoni F, Giordano A, Ferriero G. Rasch analysis of the short form 8-item Parkinson’s Disease Questionnaire (PDQ-8) Quality of Life Research. 2008;17:541–548. doi: 10.1007/s11136-008-9341-6.
    1. Hawthorne G, Densley K, Pallant JF, Mortimer D, Segal L. Deriving utility scores from the SF-36 health instrument using Rasch analysis. Quality of Life Research. 2008;17:1183–1193. doi: 10.1007/s11136-008-9395-5.
    1. Davidson M. Rasch analysis of 24-, 18- and 11-item versions of the Roland-Morris Disability Questionnaire. Quality of Life Research. 2009;18:473–481. doi: 10.1007/s11136-009-9456-4.
    1. Ramp M, Khan F, Misajon RA, Pallant JF. Rasch analysis of the multiple sclerosis impact scale MSIS-29. Health and Quality of Life Outcomes. 2009;7:58. doi: 10.1186/1477-7525-7-58.
    1. Young TA, Rowen D, Norquist J, Brazier JE. Developing preference-based health measures: Using Rasch analysis to generate health state values. Quality of Life Research. 2010;19:907–917. doi: 10.1007/s11136-010-9646-0.
    1. Tang K, Beaton DE, Lacaille D, et al. The work instability scale for rheumatoid arthritis (RA-WIS): Does it work in osteoarthritis? Quality of Life Research. 2010;19:1057–1068. doi: 10.1007/s11136-010-9656-y.
    1. Rasch G. Probalistic models for some inteligence and attainment tests. Chicago: The University of Chicago, Expanded Edition; 1960.
    1. Linacre JM, Wright BD. A User’s Guide to WINSTEPS: Rasch model computer program. Chicago, Il: MESA Press; 2000.
    1. Wright, B. D., & Linacre, J. M. (1994). Reasonable mean-square fit values. Rasch Measurement Transactions. p. 370. .
    1. Fisher Jr, W. P. (1992). Reliability statistics. Rasch Measurement Transactions. p. 238. .
    1. Wright, B. D., Masters, G. (2002). Number of person or item strata. Rasch Measurement Transactions. p. 888. .
    1. Linacre JM. Investigating rating scale category utility. Journal of Outcome Measurement. 1999;3:103–122.
    1. Lindeboom JA, Bruijnesteijn van Coppenraet ES, Kuijper EJ, et al. Interpretation and precision of the Observer Scar Assessment Scale improved by a revised scoring. Journal of Clinical Epidemiology. 2008;61:1289–1295. doi: 10.1016/j.jclinepi.2008.04.001.

Source: PubMed

Sponsorer och medarbetare

Medicinska tillstånd

Läkemedelsinterventioner

3
Prenumerera