Performance of an item response theory-based computer adaptive test in identifying functional decline.

Objective: To achieve a low respondent burden and increase the responsiveness of functional measurement by using an item response theory-based computer adaptive test (CAT), the Activity Measure for Post-Acute Care (AM-PAC) CAT.

Design: Two-year prospective cohort study.

Setting: Telephonic assessments from a quaternary medical center.

Participants: Patients (N=311) with late-stage lung cancer (LC).

Interventions: Monthly assessments for up to 2 years. Disease progression was determined via record abstraction. Anchor-based responsiveness techniques were used to compare AM-PAC-CAT score changes between global rating of change (GRC) question response levels, as well as between intervals when adverse clinical events or symptom worsening did and did not occur. Distribution-based responsiveness assessments included calculation of the standardized effect size (SES) and standardized response mean (SRM).

Main Outcome Measures: AM-PAC-CAT, symptom numerical rating scales, and a GRC.

Results: Administration time averaged 112 seconds over 2543 interviews. AM-PAC-CAT score changes became more positive as GRC responses reflected more improved states: a lot worse (-11.62), a little worse (-1.92), the same (-.10), a little better (1.01), and a lot better (2.82). Score changes were negative when associated with adverse clinical events. The SES and SRM for score differences between 1 to 2 and 9 to 10 months prior to death were -.87 and -1.13, respectively. The minimally important difference estimate was defined by the mean CAT session SE at 2.0.

Conclusions: The AM-PAC-CAT imposes a low, <2-minute, respondent burden, and distribution- and anchor-based methods suggest that is moderately responsive in patients with late-stage LC.