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Health and Quality of Life Outcomes BioMed Central Research Open Access Classical test theory

Health and Quality of Life Outcomes BioMed Central Research Open Access Classical test theory versus Rasch analysis for quality of life questionnaire reduction Luis Prieto*1, Jordi Alonso2 and Rosa Lamarca2 Address: 1Health Outcomes Research Unit. Eli Lilly and Company, Madrid, Spain and 2Health Services Research Unit. Institut Municipal d'Investigació Mèdica (IMIM). C/ Dr. Aiguader, 80; 08003 Barcelona, Spain Email: Luis Prieto* - prieto_luis@lilly.com; Jordi Alonso - jalonso@imim.es; Rosa Lamarca - rlamarca@imim.es * Corresponding author Published: 28 July 2003 Health and Quality of Life Outcomes 2003, 1:27 This article is available from: http://www.hqlo.com/content/1/1/27 Received: 11 April 2003 Accepted: 28 July 2003 © 2003 Prieto et al; licensee BioMed Central Ltd | BioMed Central Health and Quality of Life Outcomes Research Open Access Classical test theory versus Rasch analysis for quality of life questionnaire reduction Luis Prieto 1 Jordi Alonso2 and Rosa Lamarca2 Address 1Health Outcomes Research Unit. Eli Lilly and Company Madrid Spain and 2Health Services Research Unit. Institut Municipal d Investigació Mèdica IMIM . C Dr. Aiguader 80 08003 Barcelona Spain Email Luis Prieto - prieto_luis@lilly.com Jordi Alonso - jalonso@imim.es Rosa Lamarca - rlamarca@imim.es Corresponding author Published 28 July 2003 Received 11 April 2003 Accepted 28 July 2003 Health and Quality of Life Outcomes 2003 1 27 This article is available from http www.hqlo.cOm content 1 1 27 2003 Prieto et al licensee BioMed Central Ltd. This is an Open Access article verbatim copying and redistribution of this article are permitted in all media for any purpose provided this notice is preserved along with the article s original URL. Abstract Background Although health-related quality of life HRQOL instruments may offer satisfactory results their length often limits the extent to which they are actually applied in clinical practice. Efforts to develop short questionnaires have largely focused on reducing existing instruments. The approaches most frequently employed for this purpose rely on statistical procedures that are considered exponents of Classical Test Theory CTT . Despite the popularity of CTT two major conceptual limitations have been pointed out the lack of an explicit ordered continuum of items that represent a unidimensional construct and the lack of additivity of rating scale data. In contrast to the CTT approach the Rasch model provides an alternative scaling methodology that enables the examination of the hierarchical structure unidimensionality and additivity of HRQOL measures. METHODS In order to empirically compare CTT and Rasch Analysis RA results this paper presents the parallel reduction of a 38-item questionnaire the Nottingham Health .