NEW YORK (Reuters Health) -- The widely cited estimate that one in three Vietnam veterans suffered post-traumatic stress disorder as a result of their service may be too high, researchers are reporting.
In a detailed re-analysis of a 1988 U.S. government study, researchers found that the figure is probably closer to 20 percent, with about 9 percent of vets still showing PTSD symptoms a dozen years after the war ended.
The 1988 study had estimated that 15 percent of veterans were still suffering from the disorder at the time.
The new figures, published in the journal Science, come years after critics began charging that the 1988 estimates had to be inflated. One argument was that, with only 15 percent of troops in Vietnam serving in combat roles, it was improbable that more than 30 percent would develop PTSD.
Despite the new downward adjustments, however, the study authors say their findings still support the general message from the earlier study: that the Vietnam War took a "severe psychological toll" on veterans -- not only combat soldiers, but support troops as well.
"We didn't do this study to resolve the controversy" over the earlier figures, said lead researcher Dr. Bruce P. Dohrenwend of the New York State Psychiatric Institute and Columbia University School of Public Health in New York City.
Indeed, he told Reuters Health he thinks media reports have made too much of the lower PTSD numbers. His team's estimate of Vietnam's psychological toll is "still very substantial," Dohrenwend said.
People with PTSD suffer nightmares, flashbacks, emotional numbness and other difficulties in response to a life-threatening event or witnessing such a trauma. There are several reasons the new analysis found fewer veterans had the disorder than previously estimated.
For the original study, researchers interviewed 1,200 Vietnam vets across the country, and gave in-depth diagnostic interviews to 260 of them. They concluded that 30.9 percent had suffered PTSD at some time since the war, and that 15.2 still were.
Dohrenwend's team conducted a more rigorous analysis; besides examining records and recordings from the original study's diagnostic interviews, they used extensive military records that weren't available at the time of the 1988 study to corroborate veterans' exposure to combat stress.
The researchers found that in some cases, veterans who were diagnosed with PTSD in the original study had symptoms that did not substantially impair their daily functioning -- a point that is used in PTSD diagnosis now, but not in the 1988 study.
In other cases, vets' psychological difficulties actually began before their Vietnam service, and not in response to their war experience.
The researchers found no evidence, however, of veterans exaggerating or lying about their combat experience.
In the end, Dohrenwend and his colleagues concluded that 18.7 percent of the study participants suffered PTSD as a result of their service.
The Vietnam War and the ongoing conflict in Iraq share some similarities, Dohrenwend pointed out -- including the absence of traditional "fronts," and the difficulty that soldiers can have telling innocent civilians from the enemy.
The new PTSD estimates may offer a clearer picture of what to expect from soldiers returning from Iraq, according to Dohrenwend. "That's what I hope we're doing," he said.