Dimensionality of the posttraumatic stress response among police officers and fire fighters: an evaluation of two self-report scales.

Confirmatory factor analyses were done to assess the dimensionality of the stress response in a sample of police officers and fire fighters (n = 1,168) involved in the 1992 air disaster in Amsterdam. The confirmatory factor analyses were applied to the responses on two psychometrically different instruments, i.e., the Self-Rating Inventory for Posttraumatic Stress Disorder (SRIP) and the Impact of Event Scale (IES). The previously found distinction between (active) avoidance and numbing in samples highly affected by posttraumatic stress disorder appears to be applicable to the stress response of a less affected sample. For the SRIP, a five-factor structure (i.e., intrusion, avoidance, hyperarousal, emotional numbing and sleep disturbance) appeared to fit slightly better than the four-factor structures from previous findings. For the IES, our results replicated findings of a four-dimensional structure (i.e., intrusion, avoidance, numbing and sleep disturbance) underlying the posttraumatic stress response. The factors of the best-fitting structure of both instruments proved reliable. Due to the psychometric properties of the two instruments, the relationship between similar factors in both instruments was only low to moderate. Compared with the IES, factors of the SRIP were, however, less discriminative from other symptoms of psychopathology. Replication in different traumatized or community samples is recommended.