You will notice that there are several versions of many of the PROMIS short forms (e.g., the "original" 1.0 short form, as well as the 4a, 6a, and 8a versions).The original short forms were constructed by the domain teams.  The goal was to identify 6-8 items that represented the range of the trait and also represented the content of the item bank.  Domain experts reviewed short forms to give input on the relevance of each item.  Each domain group worked independently and those original short forms are 6-10 items long.  Psychometric properties and clinical input were both used and likely varied in importance across domains. 

            Later, we developed the PROMIS Profile instruments.  This is a collection of short forms for 7 PROMIS domains. PROMIS constructed “high information” PROMIS short forms for seven domains (Anxiety, Depression, Sleep Disturbance, Fatigue, Pain Interference (Impact), Physical Function, and Satisfaction with Participation in Social Roles). For each domain, 4-item, 6-item and 8-items have been selected so that the items are nested/overlap (e.g., the 8-item form is the 6-item form plus two additional items). The selection of items was in part based on two sets of rankings of items within each domain using two psychometric criteria: (1) maximum interval information; and 2) CAT simulations. Item rankings were similar for both criteria. For the maximum interval criterion, each item information function was integrated (without weighting) for the interval from the mean to 2 SDS worse than the mean. For the CAT simulations, responses to all items in each bank were generated using a random sample of 1,000 simulees drawn separately for each bank (centered on 0.5 SD worse than the general population mean). Items were rank ordered based on their average administration rank over the simulees. Content experts reviewed the items and rankings and made cuts of 4, 6, and 8 items.