An Item Response Theory Analysis of the Clinician-Administered PTSD Scale for DSM-5 Among Veterans

We used item response theory (IRT) analysis to examine Clinician-Administered PTSD Scale for DSM-5 (CAPS-5) item performance using data from three large samples of veterans (total N = 808) using both binary and ordinal rating methods. Relative to binary ratings, ordinal ratings provided good coverage from well below to well above average within each symptom cluster. However, coverage varied by cluster, and item difficulties were unevenly distributed within each cluster, with numerous instances of redundancy. For both binary and ordinal scores, flashbacks, dissociative amnesia, and self-destructive behavior items showed a pattern of high difficulty but relatively poor discrimination. Results indicate that CAPS-5 ordinal ratings provide good severity coverage and that most items accurately differentiated between participants by severity. Observed uneven distribution and redundancy in item difficulty suggest there is opportunity to create an abbreviated version of the CAPS-5 for determining PTSD symptom severity, but not DSM-5 PTSD diagnosis, without sacrificing precision.