Current issues in psychometric assessment of outcome measures

medicina fluminensis 2012, Vol. 48, No. 4, p. 463-470 463 Abstract. In recent years there has been an increasing use of outcome measures in clinical practice, audit procedures and quality control. The psychometric assessment of these measures is still largely based on classical test theory (CTT), including analysis of internal consistency, reproducibility, and criterion-related validity. But this approach neglects standard criteria and practical attributes that need to be considered when evaluating the fundamental properties of a measurement tool. Conversely, Rasch analysis (RA) is an original item-response theory analysis based on latent-trait modelling, and provides a statistical model that prescribes how data should be in order to comply with theoretical requirements of measurement. RA gives psychometric information not obtainable through CTT, namely: (i) the functioning of rating scale categories; (ii) the measure’s validity, e.g. how well an item performs in terms of its relevance or usefulness for measuring the underlying construct, and the consistency of item difficulty compared with the expectations of the construct; (iii) the reliability, in terms of ‘separation’; and (iv) the dimensionality of the scale and analysis of local independence of items. For these reasons, RA is increasingly used and it was recently recommended as a method for assessing scale properties in addition to classical psychometric criteria for reviewing and assessing surveys and questionnaires for disability outcomes research. The purpose of this paper is to provide some insights regarding the use of modern psychometric approaches such as RA for selecting and/or revising outcome measures in Physical and Rehabilitation Medicine.