CONSTRUCT-VALIDATION AND THE RASCH MODEL - FUNCTIONAL ABILITY OF HEALTHY ELDERLY PEOPLE

The purpose of this study was to test the construct validity of a meas ure of functional ability, developed with the intention of achieving a high degree of variability and capacity for discriminating among a gr oup of healthy elderly people. Data were collected from 734 70-year-ol d people in Denmark in the county of Copenhagen. Functional ability wa s measured with the traditional activities of daily living and with a classification system developed specially for healthy elderly people. Construct validity was tested by the Rasch model for item analysis, ad dressing specifically the internal validity by assessing the homogenei ty of items under different conditions. The results show that the prop osed measure of functional ability is a combination of six different d imensions, divided into 3 types: mobility function, lower limb functio n and upper limb function. With regard to these three types decreased functional ability can appear by either tiredness or reduced speed.