Functional Capacity Index in Elderly: Construction through the Item Response Theory

Background: The aim of the present study was to apply item response theory
to measure the functional capacity index as an important measure of the
component of positive aspects of functionality among elderly people, contributing to the expansion of the use of this tool by creating shorter and more precise scales for analysis of health situations. Methods: Cross-sectional
study was performed, and sample consisted of 41,269 elderlies aged 60 or
more from the 27 federal units that participated in the National Household
Sample Survey, in 2008, in Brazil. The generalized partial credit model was
used for the calibration of items. Results: The results of the analysis showed
that the functional capacity index was sufficiently unidimensional for item
response theory and, for greater reliability, the inclusion of more difficult
items for elderly Brazilians with better functional capacity would be required.
Conclusions: Finally, the present study argues that the functional
capacity index can be used as a tool in the analysis and prioritization of health
situations.