The Impact of Event Scale (IES) was developed by Horowitz, Wilner, and Alvarez (1979) in order to assess the frequency of posttraumatic stress symptoms experienced during the past week. The scale consisted of 15 items rated on a 4point scale namely, 0 (not at all), 1 (rarely), 3 (sometimes), and 5 (often). IES includes two subscales namely intrusion and avoidance with internal reliability coefficients of .79 and .82, respectively (Horowitz et al., 1979).

Intrusion and avoidance subscales of the IES were not sufficient to characterize Posttraumatic Stress Disorder according to DSMIIIR, therefore Weiss and Marmar (1997) revised the scale and 6 items characterizing hyperarousal symptoms and 1 item characterizing intrusion were added to the scale. Therefore, the number of item was increased to 22 and the name of the scale changed to Impact of Event ScaleRevised. IESR includes intrusion, avoidance, and hyperarousal subscales. Weiss and Marmar (1997) reported high levels of internal reliability of intrusion (α = .87), avoidance (α = .84), and hyperarousal (α = .79) subscales.

The Turkish translation and adaptation of the scale was performed by Işıklı (2006). In this Turkish version, the scale was rated on a 5point scale ranging from 0 (never) to 4 (very much). Cronbach’s alpha coefficients of hyperarousal, intrusion, and avoidance subscales were .90, .83, and .82, respectively. The internal reliability of the total scale was reported as very high (α= .93). In the present study, the IESR was used to measure posttraumatic stress level of participants after the traffic accident. The internal reliability of intrusion, avoidance, and hyperarousal subscales were .92, .81, and .89, respectively. The reliability coefficient of the total scale was .94. The IESR is presented in Appendix F.