Figure 2

Option characteristic curves and expected item total score for Item 1: Delusions. Option characteristic curves (solid lines) and expected item total score (dashed line) are plotted as a function of scores on the Positive Symptomatology Subscale form the PANNS, expressed as standard normal scores (lower x-axis) and expected total scores (upper x-axis). The probability of endorsing an option characteristic curve (solid lines) is scaled on the left y-axis and the expected item score (dashed line) is scaled on the right y-axis. Many features of an ideal item are evident in this plot.