The Groningen Activity Restriction Scale for measuring disability: its utility in international comparisons.

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Abstract
OBJECTIVES. The Groningen Activity Restriction Scale (GARS) is a non-disease-specific instrument to measure disability in activities of daily living (ADL) and instrumental activities of daily living (IADL). It was developed in studies of Dutch samples consisting of elderly or chronically ill people. The psychometric properties of the GARS demonstrated in these studies were highly satisfactory. This paper addresses the psychometric properties of the GARS across countries. METHODS. Data of 623 patients with recently diagnosed rheumatoid arthritis from four European countries were analyzed by means of a principal components analysis and a Mokken scale analysis for polychotomous items. RESULTS. The results of the analyses were highly satisfactory: there was one strong and reliable general factor representing one underlying dimension of disability in ADL and IADL, and there was a clear hierarchical ordering of the items included in the GARS. The validity of the GARS was strongly suggested by the pattern of associations of the GARS with age, sex, and other existing health status measures. CONCLUSIONS. The psychometric characteristics of the GARS, which measures disability in ADL and IADL simultaneously, make this instrument very useful for comparative research across countries.