An exploratory analysis of functional staging using an item response theory approach

Area of Science:

• Rehabilitation Medicine
• Psychometrics
• Health Services Research

Background:

• Functional staging systems are crucial for assessing patient recovery post-rehabilitation.
• Existing systems, like the FIM instrument, have limitations in capturing nuanced functional changes.
• Item Response Theory (IRT) offers a sophisticated psychometric approach for developing robust measurement tools.

Purpose of the Study:

• To develop and assess the feasibility of an IRT-based functional staging system using short forms of the AM-PAC.
• To compare the criterion validity and sensitivity of the IRT-based AM-PAC staging system against a non-IRT-based FIM staging system.
• To evaluate the system's effectiveness in classifying patients' functioning performance over time.

Main Methods:

• A prospective, longitudinal cohort study was conducted with 516 patients undergoing inpatient rehabilitation.
• Patients were interviewed at hospital discharge and at 1, 6, and 12 months post-discharge, with follow-ups in their homes.
• The study utilized short forms of the AM-PAC for mobility, daily activities, and cognitive skills, comparing outcomes to FIM stages.

Main Results:

• Meaningful IRT-based staging definitions and cut scores were successfully developed using AM-PAC short forms.
• The IRT-based AM-PAC stages demonstrated comparable or superior correlation with criterion items versus FIM stages.
• Both staging systems showed sensitivity to change; FIM stages were better at early detection, while AM-PAC stages were more discriminant in later follow-ups.

Conclusions:

• An IRT-based functional staging approach using AM-PAC is feasible and effective for long-term patient classification.
• This methodology holds potential for enhancing scores from IRT-based computerized adaptive testing.
• The findings support the use of IRT for developing advanced functional assessment tools in post-acute care.