Evaluation of the Mississippi PTSD Scale--Revised using Rasch measurement.

This study used Rasch measurement theory to examine the Mississippi Scale--Revised for its utility in the development of an interval measure of posttraumatic stress disorder (PTSD). Rasch is a probability-based theory that provides both a measure of the person responding to the instrument and the location of each item calibration on one common construct or dimension. The study used a largely male sample of 153 veterans to evaluate the quality of the items defining PTSD, to describe how the items represent the symptom range of the disorder, and to assess the functioning of items in evaluating PTSD with and without comorbid MDD. Sixteen items were found to fit the measurement model. These items may be used to develop an interval scale of the PTSD construct that is generalizable across diverse populations and that can be used for individualized comparable assessments.