Factor structure of posttraumatic stress disorder as measured by the Impact of Event Scale–Revised: Stability across cultures and time.

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This study examined the structure of posttraumatic stress disorder (PTSD) as measured by the Impact of Event Scale–Revised (IES-R; Weiss & Marmar, 1997), tested factorial invariance for samples of 235 Israeli emergency room patients and 306 U.S. undergraduate students, and then evaluated factorial invariance over multiple occasions within the emergency room sample. A four-factor structure representing intrusion, avoidance-numbing, hyperarousal, and sleep emerged as the preferred model. Configural invariance over groups was supported for this model. Likewise, configural invariance over occasions was demonstrated, but metric invariance was not fully supported, with variation in the loadings on the intrusion factor over time seemingly the source of misfit. Interpretations and conclusions center on sleep as a separate factor underlying the structure of the IES-R, the distinction between avoidance and numbing as a function of how the IES-R (vs. the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition) operationalizes the numbing feature of PTSD and possible shifts in the meaning of intrusion over time.