Rasch analysis of the Multiple Sclerosis Impact Scale (MSIS-29)
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Rasch analysis of the Multiple Sclerosis Impact Scale (MSIS-29) Melina Ramp*1, Fary Khan2, Rose Anne Misajon3 and Julie F Pallant4 Address: 1Department of General Practice, University of Melbourne, 200 Berkeley Street, Carlton 3053, Victoria, Australia, 2Department of Rehabilitation Medicine, University of Melbourne, Royal Melbourne Hospital, Melbourne, Australia, 3School of Political and Social Inquiry, Monash University, Melbourne, Australia and 4School of Rural Health, University of Melbourne, 49 Graham Street, Shepparton 3630, Victoria, Australia Email: Melina Ramp* - [email protected]; Fary Khan - [email protected]; Rose Anne Misajon - [email protected]; Julie F Pallant - [email protected] * Corresponding author
Published: 22 June 2009 Health and Quality of Life Outcomes 2009, 7:58
doi:10.1186/1477-7525-7-58
Received: 21 December 2008 Accepted: 22 June 2009
This article is available from: http://www.hqlo.com/content/7/1/58 © 2009 Ramp et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract Background: Multiple Sclerosis (MS) is a degenerative neurological disease that causes impairments, including spasticity, pain, fatigue, and bladder dysfunction, which negatively impact on quality of life. The Multiple Sclerosis Impact Scale (MSIS-29) is a disease-specific health-related quality of life (HRQoL) instrument, developed using the patient's perspective on disease impact. It consists of two subscales assessing the physical (MSIS-29-PHYS) and psychological (MSIS-29PSYCH) impact of MS. Although previous studies have found support for the psychometric properties of the MSIS-29 using traditional methods of scale evaluation, the scale has not been subjected to a detailed Rasch analysis. Therefore, the objective of this study was to use Rasch analysis to assess the internal validity of the scale, and its response format, item fit, targeting, internal consistency and dimensionality. Methods: Ninety-two persons with definite MS residing in the community were recruited from a tertiary hospital database. Patients completed the MSIS-29 as part of a larger study. Rasch analysis was undertaken to assess the psychometric properties of the MSIS-29. Results: Rasch analysis showed overall support for the psychometric properties of the two MSIS29 subscales, however it was necessary to reduce the response format of the MSIS-29-PHYS to a 3-point response scale. Both subscales were unidimensional, had good internal consistency, and were free from item bias for sex and age. Dimensionality testing indicated it was not appropriate to combine the two subscales to form a total MSIS score. Conclusion: In this first study to use Rasch analysis to fully assess the psychometric properties of the MSIS-29 support was found for the
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