Psychometric Evaluation of an ICF-Based Instrument to Assess Work Ability in Occupational Health Care

Occupational health professionals (OHPs) collaborate to support return to work (RTW) for employees on long-term sick leave, but differences in roles and perspectives can result in inconsistent work ability assessments. To promote a shared understanding of work ability, the ICF (International Classification of Functioning, Disability, and Health)-based Work Ability & Reintegration Description (WARD) instrument was developed. This study evaluated its psychometric properties, in particular criterion validity and reliability.

A mixed-methods study was conducted in three phases. Firstly, a reference standard set for assessing work ability in 10 case vignettes was established employing the Modified Delphi method with nine OHPs. Secondly, 22 OHPs independently assessed work ability with the WARD-instrument, for which overall agreement with the reference standard, and inter-rater reliability were calculated. Thirdly, a focus group with eight OHPs explored sources of variation for assessing work ability with WARD.

Agreement with the reference standard ranged from 58.6% to 99.5%. High agreement (> 70%) was found for 23 out of 29 items. Specificity (59.7%-99.5%) generally exceeded sensitivity (18.2%-95.5%), indicating greater consistency in ruling out non-relevant items than in identifying relevant ones. Focus group discussions emphasized that assessments should be context-dependent to support rehabilitation purposes.

The WARD-instrument shows promising criterion validity and reliability, especially for objectifiable and physical aspects of functioning. More complex and context-dependent domains, such as cognitive aspects of functioning and personal factors, remain challenging to consistently assess among different OHPs. Its focus on identifying context-sensitive RTW barriers may support more person-centered sick leave guidance. Further research in real-life practice is needed to strengthen validation and guide implementation.