Figure 1 presents items characteristics curves (ICC) of WHOQOL-OLD.
The de-motivation questionnaire consists of 35 statements gauging six demotivators: teachers (6 items), characteristics of classes (7 items), class environment (7 items), class materials (6 items), lack of interest (4 items), and experiences of failure (5 items).
Most items operated in the high expectations part of the items characteristics curves (ICC).
Data will be considered MAR if the probability of missing data may depend on covariates describing the patients or on items characteristics [ 13, 17].
In addition, we visually inspected whether the model-expected item characteristic curve fit the (non-parametric) observed item characteristic curve.
It also can be depicted in an item characteristic curve, as in Figure 3. Figure 3 Item characteristic curves for a dichotomous Rasch model with three items of varying difficulty (See Rost, 2004, p. 125; Winther, 2010a, p. 41).
The quality of single items was examined in several item-specific analyses, including analyses of item fit statistics, item characteristic curves, and item-total correlations.
Obviously, an item displays DIF if the item characteristic curve differs for different groups or, similarly, when each/any of the item parameters differs across groups.
