Figure 1From: Item response analysis of the Positive and Negative Syndrome Scale Option characteristic curves for an ideal item. The probability of endorsing an individual option (y-axis) from this idealized item is plotted as a function of expected total scores (upper x-axis) and standard normal quantiles (lower x-axis). Expected total scores show the level of symptom severity at which different options are endorsed. Standard normal quantiles, which are analogous to z-scores, show the proportion of the sample at different levels of expected total scores. Key features of this idealized item are described in the main text.Back to article page