NEW YORK (AP) -- Researchers studying the psychological effect of the events of Sept. 11 on New Yorkers estimated that more than 150,000 residents suffered post-traumatic stress disorder or depression following the World Trade Center attack.

"New Yorkers together went through a severe trauma," said Dr. Sandro Galea, an author of the study, published in Thursday's New England Journal of Medicine. He said the study demonstrates "there are tremendous mental health needs."

Out of a representative sample of adults surveyed, researchers from the New York Academy of Medicine found that 7.5 percent of those living in the southern part of Manhattan suffered post-traumatic stress disorder. An additional 9.7 percent reported symptoms the researchers defined as depression.

In the trade center's immediate neighborhood, the prevalence of post-traumatic stress was particularly high - 20 percent - researchers said.

The 988 respondents of the survey, which was paid for by the nonprofit September 11th Fund, were selected at random for phone interviews from Oct. 16 to Nov. 15 and they represent a sample of the population.

Marylene Cloitre, professor of psychology at Cornell University's Weill Medical College and director of the Institute for Anxiety and Traumatic Stress, said surveying people five to eight weeks after the attack was significant because stress disorder usually arises within three months.

"This was the slice of time where we find, presumably, the highest rates of PTSD," Cloitre said.

She warned the rates could climb: "Displacement from home and economic difficulties contribute to the development of PTSD and those factors hadn't completely emerged by this point."

Additional surveys were conducted at the four- and six-month marks after the attacks; the findings are still being reviewed. The four-month survey was expanded to include all of New York City, and the six-month review encompassed the entire metropolitan area. The researchers also plan a one-year study.

Post-traumatic stress disorder symptoms include nightmares, anxiety, irritability or outbursts of anger. The symptoms are usually present for at least a month. Feelings of intense guilt are also common.

Symptoms of depression can include loss of interest in life, loss of appetite, sleeping irregularities, trouble concentrating and feelings of guilt or worthlessness.

Dr. Neal Cohen, former city health commissioner, said the report should encourage people "to recognize there is something normal - not aberrant - about their response to these events and they may benefit from professional care."

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