Psychometric properties of self-administered Lequesne Algofunctional Indexes in patients with hip and knee osteoarthritis: an evaluation using classical test theory and Rasch analysis.

The aim of this study is to perform a psychometric analysis of the Lequesne Algofunctional Indexes (LAI) for the severity of osteoarthritis (OA) of the hip (LAI-hip) and knee (LAI-knee), using classical test theory (CTT) and Rasch analysis. Questionnaires were completed by 1,214 patients with symptomatic OA of the knee (n = 697) and hip (n = 517). Internal consistency was evaluated using Cronbach's alpha and an item-to-total correlation. Dimensionality was investigated with a factor analysis. Raw scores underwent Rasch analysis. Cronbach's alpha was 0.84 for LAI-hip and 0.82 for LAI-knee. LAI-hip resulted in unidimensionality according to the factor analysis, while LAI-knee supported both a single and a two-factor solution (items 1-6b and 7-10, respectively). At Rasch analysis, the rating categories of item 'maximum distance walked' did not comply with the criteria for category functioning in either LAI-hip or LAI-knee. A test of the residual correlation showed item dependency in both LAI-hip and LAI-knee. Misfitting items were present in both the scales. According to both CTT and Rasch analysis, in our two samples representing a wide spectrum of both hip and knee OA severity the LAI-hip and LAI-knee showed a series of drawbacks, which rendered both questionnaires inadequate in relation to their metric properties and severely limit their ability to perform, as a composite measure, in line with the main aims of their developers.