Description
The IES-R was designed as a measure of post-traumatic stress disorder (PTSD) symptoms, and is a short, easily administered self-report questionnaire. It can be used for repeated measurements over time to monitor progress. It is best used for recent and specific traumatic events. It has 22 questions, 5 of which were added to the original Horowitz (IES) to better capture the DSM-IV criteria for PTSD (Weiss & Marmar, 1997). It is an appropriate instrument to measure the subjective response to a specific traumatic event in an adult or senior population. There are three subscales: intrusion (intrusive thoughts, nightmares, intrusive feelings and imagery, dissociative-like re-experiencing), avoidance (numbing of responsiveness, avoidance of feelings, situations, and ideas), and hyperarousal (anger, irritability, hypervigilance, difficulty concentrating, heightened startle), as well as a total subjective stress IES-R score.

Validity
The IES-R was designed and validated using a specific traumatic event as a reference in the directions to the patient while administering the tool and while using a specific time frame of the past seven days. The scale discriminates between a variety of traumatized groups from non-traumatized groups in general population studies. The subscales of avoidance and intrusion show good internal consistency. While related, the subscales measure different dimensions of stress response. African-Americans have been shown to score higher than European-Americans on the IES in general population studies, an effect that diminished with increasing relative violence. This finding should be taken into account during interpretation. The hyperarousal subscale added by Weiss and Marmar has good predictive validity with regard to trauma (Briere, 1997), while the intrusion and avoidance subscales detect relevant differences in the clinical response to traumatic events of varying severity. Sundin and Horomitz (2002) showed that the IES’s two-factor structure is stable over different types of events, that it can discriminate between stress reactions at different times after the event, and that it has convergent validity with observer-diagnosed post-traumatic stress disorder.

Interpretation
Results consist of a total raw score, and raw scores for three subscales: The Avoidance Scale, Intrusion Scale, and the Hyperarousal Scale. Additionally the mean rating for the total score and each subscale is presented, which gives an indication of the level of impairment from post traumatic stress, where:

0 = No symptoms
1 = Few symptoms
2 = Moderate symptoms
3 = A High level of symptoms
4 = An Extremely high level of symptoms

Developer
Weiss, D.S., & Marmar, C.R. (1997). The Impact of Event Scale-Revised. In J.P. Wilson, & T.M. Keane (Eds.), Assessing Psychological Trauma and PTSD: A Practitioner’s Handbook (pp. 399-411). New York: Guilford Press.The original Impact of events Scale (IES) was developed in the 1980s