Fig. 4

WEMWBS Item Characteristic Curves (ICC) and Item Information Function (IIF) (N = 386). ICC plots demonstrate how the probability of endorsing a category of WEMWBS items (i.e., none of the time to all of the time) change as levels of the latent trait change. IIF plots demonstrate how reliability indices vary with changes in the latent trait. Note: ICC expresses in a nonlinear (logit) regression line pertaining to difficulty (β) and discrimination (α) parameters. Difficulty (β) indicates the level of the latent trait where there is a .5 probability that a participant will endorse a specific criterion or item [85]. For example, ‘easier’ items have lower β values and their ICC is represented closer to the horizontal axis. For clarification purposes, those endorsing easier items are said to have lower SWB. Conversely, those who endorse the difficult items are said to have higher SWB ([26, 85]). Discrimination (α) describes how steeply the rate of success (positive response) of an individual varies according to their latent trait levels. Thus, items more strongly related to the latent variable present steeper ICC functions [85]