The Psychometric Properties of the International Work Addiction Scale (IWAS) Using CTT and IRT in a Nationally Representative UK Sample

Work addiction refers to a compulsive drive to work relentlessly, leading to personal harm, distress, and impaired relationships. It has been characterised by salience, mood modification, tolerance, withdrawal, conflict, relapse and problems. Despite scholarly attention, it is not formally recognised within the current versions of existing diagnostic manuals. This study examined the interpretation and research use of scores from the seven-item (IWAS-7) and five-item (IWAS-5) versions of the International Work Addiction Scale (IWAS) across two samples from the United Kingdom (UK): a non-representative employee sample ( n = 245, M age = 28.93) and a nationally representative sample ( n = 1,001), with analyses focused on employed individuals ( n = 764, M age = 44.45). Evidence based on internal structure supported a unidimensional interpretation for both versions, with adequate reliability. Evidence based on relations to other variables showed strong associations between IWAS scores and the Bergen Work Addiction Scale (BWAS), and theoretically consistent relationships with relevant constructs. Scalar measurement invariance across gender substantiated comparable IWAS score interpretation for men and women, with no latent mean differences. Item response theory analyses indicated the greatest IWAS score precision at moderate-to-high work addiction levels (θ ≈ 1–3), particularly Items 5 to 7. Findings support interpreting IWAS-7 and IWAS-5 scores as brief indicators of work addiction severity for research use in UK-employed adults.