PTSD: How frequently should the symptoms occur? The effect on epidemiologic research

The definition of posttraumatic stress disorder (PTSD), like most other psychiatric disorders, relies on descriptive methodology; the formulation of the criteria needed to establish a diagnosis is based on clinical and research findings. We used our data from a community study in Beirut, Lebanon to look at the effect that the frequency of occurrence of individual PTSD symptoms might have on the total PTSD prevalence. We found that the prevalence of PTSD decreased by half if symptoms were required to have occurred at least twice per week. This phenomenon was true whether we considered war or nonwar traumata and was true for the DSM-III-R and the DSM-IV definitions of PTSD.