Standardizing Physical Function Assessments: Can We Use Different Types of Outcome Assessment Tools for Measuring a Common Construct?

• Applicant: Dr. Gregor Liegl
• Subject Area: Personality Psychology, Clinical and Medical Psychology, Methodology ; Epidemiology and Medical Biometry/Statistics ; Public Health, Healthcare Research, Social and Occupational Medicine
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 517270193

Physical function (PF) is an important outcome domain in various medical fields. Patient-reported outcome (PRO) and performance outcome (PerfO) measures are the most common PF assessment types. Many different PRO and PerfO tools measuring PF have been developed so far, making it difficult to validly compare research results. Thus, there is an urgent need for a paradigm shift away from instrument-based scoring towards construct-based assessment by calibrating insruments measuring the same construct on a standardized metric. Item response theory (IRT) modelling is a promising methodological opportunity to create construct-based item banks by calibrating any number of items measuring the same construct on a common metric. Using IRT, the Patient-Reported Outcomes Measurement Information System (PROMIS) initiative has developed a PRO-based PF item bank calibrated to a T-score metric with a general population mean of 50 and a standard deviation of 10. A main feature of PROMIS PF is that other PRO measures of PF have been calibrated to the same T-score metric, allowing for meaningful comparisons of scores across these instruments. Despite these advancements in standardizing PF assessments across different PRO measures, it is not yet possible to convert the scores of PerfO measures to PROMIS PF T-scores. Thus, PerfO measures cannot be considered when interpreting, comparing or pooling research findings based on the PROMIS PF metric. The proposed project aims to fill this gap and makes the next step forward in standardizing PF assessments by calibrating PerfO and PRO measures of PF on a standardized scale. In detail, the project has the following objectives: (1) testing whether PerfO test batteries and PRO measures of PF can be used to assess a common PF construct; (2) identification of single PerfO tasks that are suitable for assessing the specific PROMIS PF construct; and (3) extending the PROMIS PF item bank by providing IRT item parameters for appropriate PerfO items, allowing researchers and clinicians to convert PerfO results to PROMIS PF T-scores. For achieving these objectives, the German PROMIS PF item bank as well as different PerfO test batteries (Short Physical Performance Battery and three versions of the Physical Performance Test) will be administered to main target populations of PF assessments (N=800), namely geriatric patients, elderly in the general population, patients with rheumatic diseases, and patients with cardiovascular diseases. For achieving objectives (1) and (2), classical test theory as well as IRT-based methods will be used for psychometric analysis at scale and item level. For extending the PROMIS PF item bank by providing item parameters for potentially suitable PerfO tasks (objective 3), an IRT model will be fitted to the collected data, with parameters of PROMIS PF items fixed to the previously established PROMIS PF metric and with PerfO item parameters freely estimated.

• DFG Programme: Research Grants