Gender Differences in Posttraumatic Stress Symptoms After a Disaster: A Differential Item Functioning Analysis of the Impact of Event Scale-Revised

Objective: Although research indicates that women are more likely than men to report posttraumatic stress disorder (PTSD) symptoms following exposure to a disaster event, few studies have assessed whether these gender differences are due to bias in PTSD measures. Using item response theory, we conducted a differential item functioning (DIF) analysis of the widely used Impact of Event Scale-Revised (IES-R) to evaluate whether the instrument demonstrates equivalence when assessing PTSD symptoms among men and women after a major disaster (N=410). Method: We used ordinal logistic regression and item response theory modeling to investigate the presence and impact of DIF across gender groups. Results: One item (“I had waves of strong feelings about the 2011 tornado”) exhibited DIF across the subgroups for men and women. However, the magnitude of the DIF was minimal and did not produce differential measurement error at the total IES-R scale score level. Conclusion: These findings provide evidence of measurement equivalence of the IES-R and confirms its usefulness in screening for PTSD across gender groups following a disaster event.