Fig 3.

Item characteristic curve for Composite Item 2 (left) and Item 8 (right). Note. The x-axis indicates the latent trait and the y-axis indicates the item score. The black points represent the average observed item responses in each class interval. The grey logistic curve indicates the expected item responses. The slope of the Item Characteristic Curve indicates the rate of change of the expected value with respect to the latent trait at the mid-point between the minimum and maximum scores.