Background: The International Classification of Functioning, Disability and Health (ICF) offers a standardized international terminology to operationalize function management across multiple domains, but the summary score of the ICF qualifier scale provides limited information on the comparison of personal abilities and functioning difficulties.

Objectives: To enhance the interpretative power of the ICF-based Health-oriented Personal Evaluation for the community-dwelling older person (iHOPE-OP) scale through the implementation of the item response theory (IRT) modelling.

Methods: This cross-sectional, multi-centre study administrated 161 ICF categories (58 on body functions, 15 on body structures, 60 on activities or participation and 28 on environmental factors) to evaluate the functional level of 338 older citizens (female = 158, male = 180) residing in community or supportive living facilities. The validation process encompassed assessing the IRT model fitness and evaluating the psychometric properties of the IRT-derived iHOPE-OP scale.

Results: The age of participants ranged from 60 to 94.57, with the mean age of 70. The analysis of non-parametric and parametric models revealed that the three-parameter logistic IRT model, with a dichotomous scoring principle, exhibited the best fit. The 53-item iHOPE-OP scale demonstrated high reliability (Cronbach's α = 0.9729, Guttman's lambda-2 = 0.9749, Molenaar-Sijtsma Statistic = 0.9803, latent class reliability coefficient = 0.9882). There was a good validity between person abilities and the Barthel Index (p < .001, r = .83), as well as instrumental activities of daily living (p < .001, r = .84).

Conclusions: IRT methods generate the reliable and valid iHOPE-OP scale with the most discriminable and minimal items to represent the older person's functional performance at a comprehensive level. The use of the Wright map can aid in presby-functioning management by visualizing item difficulties and person abilities. IMPLICATIONS FOR PRACTICE: Considering the intricate and heterogeneous health status of older persons, a single functional assessment tool might not fulfil the need to fully understand the multifaceted health status. For use in conjunction with the IRT and ICF framework, the reliable and valid iHOPE-OP scale was developed and can be applied to capture presby-functioning. The Wright map depicts the distribution of item difficulties and person abilities on the same scale that facilitates person-centred goal setting and tailors intervention.