The American team reported that the prevalence of likely cases of posttraumatic stress disorder in the second month after the attacks was significantly higher in the New York metropolitan area than in the Washington, D.C. area (11.7 percent and 2.7 percent respectively). Other metropolitan areas and the rest of the nation had rates comparable with those seen in the Washington area (3.6 percent and 4.0 percent, respectively). Even after adjustment for sociodemographic differences between the New York City area and the rest of the country, the authors found that people in the New York metropolitan area were 2.9 times more likely than those in other areas to be probable cases of posttraumatic stress disorder.

"The terrorist attacks represent an unprecedented exposure to trauma on American soil," said lead author William E. Schlenger, PhD. "But the major burden of posttraumatic stress disorder associated with those events is closely related to direct exposure to the terrorist attacks.

"Posttraumatic stress disorder can be a long-term problem for individuals," Dr. Schlenger said. "We find people still suffering from the disorder years or even decades after the traumatic event. That is why mental health service providers, especially in New York, need to know how many people are burdened by the trauma of September 11," he said. "Early help translates to lower costs in terms of human suffering and in terms of dollars spent on public health services. At the same time, it is important to recognize that although many Americans may have been upset by the attacks of September 11, our findings suggest that by the second month after the attacks, levels of psychological symptoms had subsided to within normal ranges among those outside the New York City metropolitan area."

Study results come from an epidemiologic survey conducted in the second month following the attacks. The 2,273 adults surveyed included a national probability sample, as well as larger samples in the New York City and Washington metropolitan areas.