Applications of Item Response Theory in the Measurement of Physical Disability

• Activity Number: 517
• Type: Topic Contributed
• Date/Time: Wednesday, August 7, 2013 : 10:30 AM to 12:20 PM
• Sponsor: Committee on Statistics and Disability
• Author(s): Richard Jones*+ and Alden Gross
• Companies: Institute for Aging Research / Hebrew Senior Life and Johns Hopkins University, School of Public Health
• Keywords: Disability ; Physical performance ; Psychometrics ; Item Response Theory ; PROMIS

Abstract

Background: Item Response Theory (IRT) provides a statistical framework for measuring latent constructs.

Objective: To develop a summary composite measure of physical functioning using items from basic and independent self-reported activities of daily living and the MOS SF-12, and to scale it to a population-based normative sample.

Study Design and Setting: Disability items measured on a sample of older patients, placed on a metric linked to the Patient Reported Outcomes Measurement Information System (PROMIS) normative sample. We examined convergent validity, and predictive validity.

Results: The composite measure showed evidence for good internal reliability, accurate measurement for low and average levels of functioning, and was moderately correlated with walking speed (r=0.51) and energy expenditure (r=0.40). Less impaired scores on the composite were associated with lower rates of nursing home admission and shorter hospital length of stay.

Conclusion: Our approach is useful to directly compare physical functioning in new and existing studies using a common, population-based metric.