Psychometric properties of the Norwegian Impact of Event Scale-Revised in a non-clinical sample

Background: Despite the widespread use of the Impact of Event Scale to measure post-traumatic stress symptoms, psychometric evaluations of the scale have revealed mixed findings. Aim: The aim of the present study is to provide new empirical evidence and examine the factor structure, reliability, and predictive validity of the Norwegian version of the IES-R. Methods: Posttraumatic stress symptoms were recorded in a student sample (n=312) 3 weeks after the Southeast Asian tsunami disaster in December 2004. Confirmatory factor analyses of the IES-R behavior items using structural equation modeling (SEM) were performed on four models from existing research. Results: The original three-factor model of intrusion, avoidance and hyperarousal symptoms exhibited the best goodness-of-fit indices when defined as oblique. The IES-R also revealed satisfactory reliability. Symptom levels of intrusion and avoidance were moderate, while hyperarousal scores were low, with a significant gender difference. Conclusion: Taken together, the IES-R revealed good psychometric properties in this nonclinical student sample and could be a useful instrument to assess and follow-up on PTSD symptoms after a certain identified trauma.