Revista Facultad Nacional de Salud Pública (May 2019)
Rasch analysis of the Katz index of independence in activities of daily living in senior citizens from Antioquia, Colombia
Abstract
Improving Katz index interpretability contributes to a better understanding of its results facilitating decision making and intervention planning. Objective: To evaluate the validity of the Katz geriatric scale in senior citizens from a Rasch model perspective. Methodology: Secondary data analysis of a population-based, cross-sectional study of health status in 4,023 senior citizens conducted in Antioquia, Colombia, in 2012. Item fit, differential item functioning, unidimensionality, reliability and item-person map analyses were performed. Results: All items adjusted to the model. Transferring and Continence showed high differential item functioning with a considerable, but statistically non-significant impact on the overall estimation. Person and Item reliability were 0.80 and 0.90 respectively. The Rasch measurement explained 61.6% of variance. Conclusion: A unidimensional interval level measure can be obtained from the Katz instrument. It is important to do more research on differential functioning of Katz’s items in a way in which validity arguments on its generalization to various subpopulations could be strengthened and score interpretability could be improved.
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