Table 2 Operational Criteria for Item Selection

Criterion 1. There is a range of severity in which the majority of items is expected to be more likely scored. This is represented by the number of options for which the item was more likely to be scored than all other options.

Basis of rating: Examination of the ICCs

Ratings for Criterion 1:

Yes: Items for which ≥ 5 options are selected will be considered for inclusion the abbreviated PANSS. The cut-off of four options was selected based on the median option score of PANSS (options range from one to seven).

No: Items for which ≤ 4 options are selected.

Criterion 2. The extent to which OCCs increase rapidly with changes in overall severity. Basis of rating: Examination of the OCCs.

Ratings for Criterion 2:

Yes: The probability (y-axis of OCC curve, see Figure 1) of selecting an option increases with increasing levels of severity. E.g. the probability of option 2 being selected doubles from 0.5 to 0.25 when severity increases from a score 18 to 12.

No: The probability (y-axis of OCC curve, see Figure 1) of selecting an option does not increase with increasing levels for all options. OCCs appear flat for each option.

Somewhat: The probability (y-axis of OCC curve, see Figure 1) of selecting an option increases with increasing levels of severity from the 50^th percentile of total score.

Criterion 3. The region in which each option is more likely to be selected is ordered, left to right, in accordance with their option scores on the OCC graphs.

Basis of rating: Examination of the OCCs.

Ratings for Criterion 3:

Yes: The severity regions and corresponding severity scores. E.g. the region in which option 2 is most likely to be selected (total severity score of 7 to 25 in Figure 1), falls between the regions in which option 1 (total severity score of 7 to 20 in Figure 1) and option 3 (total severity score of 7 to 35 in Figure 1) are most likely to be selected.

No: The severity region for which an option is most likely to be scored falls outside its two adjacent options for ≥ 5 options. E.g. the severity region in which option 3 is most likely to be scored ranges from a minimum score of seven to 35, and options 2 and 4 ranges from 10 to 30.

Somewhat: The severity region for which an option is most likely to be scored falls outside its two adjacent options for ≥ 1 and ≤ 4 options.

Criterion 4. Options for an item span the full continuum of severity from seven to 40 for the Positive subscale, seven to 45 for the Negative subscale, and 16 to 80 for the General Psychopathology subscale.

Basis of rating: Examination of the OCCs

Ratings for Criterion 4:

Yes: For a particular item, all seven options span the entire range of severity (from seven to 45 for the Positive and Negative subscales and 16 to 80 for the General Psychopathology subscale).

No: Greater than or equal to four options are more likely to be selected at higher (or lower) levels of severity than corresponding options. Four options were determined as the cut-off based on the median option score of the PANSS.

Criterion 5. As in parametric IRT, the slope or steepness of the curves indicates the item's ability to discriminate individuals along the latent continuum. In nonparametric IRT, the steeper a slope of the ICC, the more discriminant the item is. Slopes were computed in TestGraf for ICC graphs of each item from the median option score (i.e. four (Moderate) on the PANSS).

Basis of rating: Examination of the slopes ICCs.

Ratings for Criterion 5:

SYes: Slope is ≥ 0.40.

No: Slope is < 0.399