Partial credit model and pivot anchoring.

This article contains information on the Rasch measurement partial credit model: what it is, how it differs from other Rasch models, when to use it, and how to use it. The calibration of instruments with increasingly complex items is described, starting with dichotomous items and moving on to polychotomous items using a single rating scale, and mixed polychotomous items using multiple rating scales, and instruments in which each item has its own rating scale. It also introduces a procedure for aligning rating scale categories to be used when more than one rating scale is used in a single instrument. Pivot anchoring is defined and an illustration of its use with the mental health scale of the SF-36 that contains positive and negative worded items is provided. It finally describes the effect of pivot anchoring on step calibrations, the item hierarchy, and person measures.