Shoop‐Worrall SJW, Voshaar MAHO, McDonagh JE, et al. - Considering that the interchangeable use of child and adult outcome measures that inaccurately capture changes over time as young people reach adulthood, researchers sought to use item response theory (IRT) to model a continuous score for functional ability that can be used regardless of which questionnaire is completed. Median age at diagnosis was 13 years in 303 adolescents and 61% were female. Mokken analyses showed high scalability, monotonicity and that each questionnaire yielded reliable scores. IRT modelling allows the direct comparison of function scores irrespective of different questionnaires being completed over time by various individuals. This facilitates ongoing function assessment as adolescents move from paediatric clinics to adult services.