Confirmatory factor analysis of the Arthritis Impact Measurement Scales 2 short form in patients with rheumatoid arthritis.

OBJECTIVE: To examine the factorial validity of the short form Arthritis Impact Measurement Scales 2 (AIMS2-SF) in patients with rheumatoid arthritis (RA). METHODS: Data were from a sample of 279 patients with active RA who completed the long form AIMS2 before starting treatment with tumor necrosis factor alpha-blocking agents. Confirmatory factor analyses were conducted to test and compare the fit of the currently used theoretical measurement model of the AIMS2-SF, originally suggested for the long form AIMS2, and 2 alternative models based on previous exploratory research. RESULTS: A model with the physical dimension divided into upper and lower body limitations was superior to the current model, and both models provided a clearly better fit than a model without a separate symptom dimension. Under the restrictive assumption of uncorrelated error terms, none of the models achieved a consistent and acceptable fit as judged by several goodness-of-fit indices. Allowing error covariances between 6 pairs of items within the same dimension resulted in an improved and acceptable fit of both the current model and the model with a separate upper and lower body component. CONCLUSION: This study generally supports the factorial validity of the AIMS2-SF and suggests the use of separate scores for upper and lower body limitations. Further research is needed to resolve the issue of high error correlations associated with particular items