BackgroundThere is little consensus on how to measure fatigue.ObjectivesTo standardize the measurement of fatigue across populations, we aimed to assess the psychometric properties of the PROMIS Fatigue item bank in the Dutch general population and obtain reference values.MethodsA sample of 1006 people participating in an internet panel completed the full v1.0 PROMIS Fatigue item bank (95 items). Structural validity (item response theory (IRT) assumptions and IRT model fit), measurement invariance/cross-cultural validity (absence of differential items functioning (DIF) for demographic variables and language, compared to data from US participants in PROMIS wave 1), and (internal) reliability (percentage of respondents with reliable estimates) were assessed.ResultsThe IRT model assumptions were considered met (ECV 0.86, Omega-H 0.92), all items fitted the IRT model, no items showed DIF for demographic variables and seven for language, but with negligible impact on T-scores. Reliable fatigue T-scores were found ...