Background The Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) is a widely used patient reported outcome in osteoarthritis. An important, but frequently overlooked, aspect of ...

Loglinear latent class models are used to detect differential item functioning (DIF). These models are formulated in such a manner that the attribute to be assessed may be continuous, as in a Rasch ...

This study investigates the stability of differential item functioning (DIF) in survey data. Surveys are conducted periodically, and their results are often reported by aggregating responses.

Overall, the WOMAC performed well with only a small number of DIF items. Five DIF items in the physical functioning subscale were initially identified and two DIF items in the pain subscale for people ...