| Sumario: | Background Assessment of physical function, a key outcome in geriatric research, relies on either patient-reported or performance-based assessments. While several patient-reported instruments have been successfully linked to the standardised Patient-Reported Outcomes Measurement Information System (PROMIS) Physical Function scale, commonly used performance-based tools, such as the Short Physical Performance Battery (SPPB), remain uncalibrated to this scale. This lack of standardisation limits interpretability, comparability, and integration of physical function data across instruments, studies, and clinical settings. Objective To link SPPB scores to the PROMIS Physical Function T-score metric in older adults. Methods This analysis is part of the Standardizing-PF project, a prospectively designed cross-sectional study examining the possibility of mapping patient-reported and performance-based assessments onto a common scale. In the present study, 556 older adults (mean age 74 years) from different clinical and community-based settings subsequently completed a generic 20-item PROMIS Physical Function short form (PROMIS-PF20a) and the SPPB. Assumptions of item response theory modelling were investigated. We estimated a unidimensional item response theory-based linking model and derived cross-walks to convert SPPB scores into standardised PROMIS PF T-scores. Results SPPB and PROMIS-PF20a were highly correlated (latent correlation = 0.89); assumptions of item response theory modelling were fulfilled. After linking, agreement between observed and linked T-scores was stable across several subsamples. Conclusions The SPPB can be meaningfully linked to the PROMIS PF T-score metric, enabling standardised interpretation, comparison, and aggregation of performance-based and self-reported physical function in older adults. We provide a user-friendly score cross-walk table to facilitate application in clinical practise and standardisation in geriatric research.
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