Extending the floor and the ceiling for assessment of physical function

Area of Science:

• Health Outcomes Research
• Rehabilitation Medicine
• Biostatistics

Background:

• Accurate assessment of physical function is crucial for evaluating health status and treatment efficacy.
• Existing measures may lack precision for individuals with very poor or very good physical function, leading to 'floor' or 'ceiling' effects.
• The Patient-Reported Outcomes Measurement Information System (PROMIS) aims to standardize health outcome measurement.

Purpose of the Study:

• To develop and validate new items for the PROMIS item bank to improve the assessment of physical function at the extreme ends of the health continuum.
• To enhance the precision of physical function assessment for individuals with extremely poor function (floor effects) and extremely good health (ceiling effects).

Main Methods:

• Development of 31 'floor' items and 31 'ceiling' items using item response theory (IRT) to supplement existing PROMIS physical function item banks.
• A 12-month prospective, observational study involving 737 participants (444 with chronic illness/older adults, 293 generally fit individuals) at health extremes.
• Calculation of effect sizes and comparison of score changes over time across new and existing measures, with back-calculation of sample size requirements.

Main Results:

• IRT analyses confirmed superior performance of the new floor and ceiling items compared to reference items (P < 0.001).
• The new items demonstrated improved ability to differentiate function at the extremes of the health spectrum.
• Estimated sample size requirements were reduced by 2-4 times for the floor population and 2 times for the ceiling population.

Conclusions:

• Expanding the range of physical function assessment items significantly enhances measurement quality and research efficiency.
• The developed items reduce the necessary sample sizes for studies involving populations at health extremes.
• This advancement supports a paradigm shift towards assessing the full spectrum of physical function, aligning medical goals with societal health objectives.