Enhancing the precision of the Mississippi Scale for Combat-Related Posttraumatic Stress Disorder: An application of item response theory.

Item response theory was used to examine the measurement qualities of the Mississippi Scale for Combat-Related Posttraumatic Stress Disorder, with data taken from the 2,348 veteran participants in the National Vietnam Veterans Readjustment Study. Using Samejima's (1969) graded response model, estimates of each item's discrimination and difficulty parameters were derived, and item and test information functions were then computed. Various item information patterns and sample items are discussed in terms of improved assessment of posttraumatic stress disorder