A reinterpretation of data from a 1988 study of Vietnam veterans has determined that their lifetime occurrence of posttraumatic stress disorder is far lower than previously thought.
The reinterpreted analysis suggests that only 19% of those veterans had a lifetime occurrence of PTSD, and that 9% were suffering from the disorder at the time of the study, which was 11–12 years after the war. The original study, based on a representative sample of 1,200 veterans, calculated a lifetime occurrence of 31%, with 15% suffering from the disorder when they were interviewed.
The National Vietnam Veterans Readjustment Study (NVVRS) relied on self-reports by the veterans on whether they experienced traumatic events, and used the DSM-III-R definition of PTSD. The new study used DSM-IV criteria and estimated exposure to traumatic events by using independent sources, such as military personnel files, military archives, and newspaper and historical accounts (Science 2006;313:979–82).
Bruce P. Dohrenwend, Ph.D., of Columbia University, New York, and colleagues applied these new estimates of military exposure to 260 of the veterans who participated in the original study. As in the original study, the investigators found a strong dose-response relationship between combat exposure and the occurrence of PTSD.
They attributed the lower estimates of PTSD occurrence to two factors. First, they eliminated individuals in whom the index traumatic event occurred before or after their service in Vietnam. Second, whereas current DSM-IV criteria for PTSD require at least some degree of social impairment to establish a diagnosis, DSM-III-R criteria in the original study had no such requirement.
Critics of the original study charged that the 31% lifetime occurrence of PTSD could not possibly be accurate, because only 15% of Vietnam veterans served in combat roles. And they said that the veterans' recall of their exposure to traumatic events could not be relied on, suggesting that access to veterans' benefits provided a motive for falsification.
The investigators involved in the reanalysis disputed both of those explanations. In comparing the self-reports of combat exposure with their objective measures, they found little evidence that the veterans falsified or exaggerated their experiences, they wrote.
For example, of the individuals judged to have low exposure to war zone stress by objective measures, 97% self-reported low exposure and only 3% reported high exposure. And of the individuals judged to have very high stress exposure by objective measures, 72% self-reported high exposure and 28% reported low exposure.
Furthermore, even though the conflict in Vietnam has been described as a “low-intensity” war for U.S. forces, it was not a conventional war with assurances of safety behind the front lines. Some military histories estimate that at least half of the veterans who served in Vietnam or its environs were involved in combat and could have been exposed to traumatic events.
“The message from the NVVRS has been that the Vietnam War took a severe psychological toll on U.S. veterans. Our results provide compelling reasons to take this message seriously,” the authors wrote. Furthermore, they pointed out, similarities exist between the combat experience in Vietnam at that time and in Iraq now.
“Both have been wars without fronts, in which it is often difficult to tell peaceful civilians from enemy combatants,” they wrotes. “What has been, and can still be, learned about PTSD and Vietnam veterans should be applicable to understanding the psychological risks to U.S. veterans of the war in Iraq.”