Linking the activity measure for post acute care and the quality of life outcomes in neurological disorders

Abstract

Objective: To use item response theory (IRT) methods to link physical functioning items in the Activity Measure for Post Acute Care (AM-PAC) and the Quality of Life Outcomes in Neurological Disorders (Neuro-QOL).

Design: Secondary data analysis of the physical functioning items of AM-PAC and Neuro-QOL. We used a nonequivalent group design with 36 core items common to both instruments and a test characteristic curve transformation method for linking AM-PAC and Neuro-QOL scores. Linking was conducted so that both raw and scaled AM-PAC and Neuro-QOL scores (mean ± SD converted-logit scores, 50 ± 10) could be compared.

Setting: AM-PAC items were administered to rehabilitation patients in post-acute care (PAC) settings. Neuro-QOL items were administered to a community sample of adults through the Internet.

Participants: PAC patients (N=1041) for the AM-PAC sample and community-dwelling adults (N=549) for the Neuro-QOL sample.

Interventions: Not applicable.

Main outcome measures: Mobility (N=25) and activity of daily living (ADL) items (N=11) common to both instruments were included in analysis.

Results: Neuro-QOL items were linked to the AM-PAC scale by using the generalized partial credit model. Mobility and ADL subscale scores from the 2 instruments were calibrated to the AM-PAC metric.

Conclusions: An IRT-based linking method placed AM-PAC and Neuro-QOL mobility and ADL scores on a common metric. This linking allowed estimation of AM-PAC mobility and ADL subscale scores based on Neuro-QOL mobility and ADL subscale scores and vice versa. The accuracy of these results should be validated in a future sample in which participants respond to both instruments.