Figure 1.

Example item characteristic curves (ICCs) exhibiting differential item functioning for the item “I felt worthless” on depression short form 8b. Theta is the depression metric on a standardized scale (M = 0, SD = 1 by definition). In this example, there are three rather than four thresholds (curve intersections); if fewer than five participants used a response category, categories were automatically collapsed by lordif. In this case, often and always were collapsed into one category.