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The purpose of this paper is to uncover the dimensional structure of a set of disability items. The analysis is based on a sample of 421 persons aged 75 years and older. Firstly, a factor analysis of the items reveals two distinct dimensions: IADL and ADL. The items with large loadings on the IADL-factor are next submitted to a Guttman analysis. An index is derived which strictly meets the requirements of a Guttman scale, but it is doubtful whether there is a true hierarchical structure among the items. The criterion validity of the index (in different versions) appears to be satisfactory when assessed in terms of the correlation with an outcome variable (home help).
Norström et al. (Tue,) studied this question.