Item Response Theory Analysis of the Texas Functional Living Scale.

OBJECTIVE

The Texas Functional Living Scale (TFLS) is a performance-based measure of functional abilities assessing the domains of time, money and calculation, communication, and memory. It is likely that certain items are more sensitive at different levels of functional impairment, with some signaling milder degrees of functional difficulty. This study analyzed psychometric characteristics of individual TFLS items using item response theory (IRT) in an outpatient clinical sample.

METHOD

In total, 270 adult outpatients completed the TFLS during clinical neuropsychological evaluation. IRT analysis using 2PL and graded response model was applied to the TFLS.

RESULTS

Item parameters, item characteristic curves, and information curves were produced. Item difficulty (a) parameters ranged from 1.05 to 2.23, and item discrimination (b) parameters ranged from -4.11 to 0.51.

CONCLUSIONS

TFLS items were differentially sensitive along the continuum of functional impairment. Items that were most sensitive to milder degrees of functional impairment involved clock drawing, microwave programming, financial calculation, and prospective memory. Other items that were optimally precise in more severe degrees of functional impairment involved interacting with a calendar and a relatively simple financial calculation task. These findings suggest that the ability to pass at least some of the items on the TFLS may not necessarily reflect fully intact functional abilities. Certain TFLS items may be able to detect the presence of subtle functional difficulties.