New Orleans' suicide rate appears to have gone up in the first six months after Hurricane Katrina evacuees were allowed back home, but the increase could be due to chance instead of post-storm depression, a study by Louisiana's epidemiologist says.

Dr. Raoult Ratard took a unique approach to studying the suicide rate because there have been no reliable estimates of how many people have returned since the storm. Various sources have put the number at anywhere from fewer than 200,000 to around 250,000 out of a pre-Katrina population of just under 455,000.

So, Ratard looked at the number of deaths from October 2005 (when the city was reopened after the storm) through March 2006, and compared that total to the number of deaths of all kinds during the same period the year before.

The pre-storm death total was 2,507; post-storm, 1,024. That means the number of deaths was down by about three-fifths.

Then Ratard looked at suicides. The number of pre-storm suicides was 16; post-storm, 11. That means the number of suicides was down by only about one-third.

So, the suicide rate appears to have gone up. But the totals are too small to conclude that Katrina caused the increase, Ratard said. "They are not big enough so that you can say with certainty that it would not be due to chance," he said.

Still, the increase indicates a troubling trend, and one that should be monitored, said Ronald Kessler, a Harvard University researcher who is studying mental health in the area.

He complimented Ratard's method for dealing with the lack of firm population numbers: "That's a clever epidemiologist!"

It is hard to say whether figures will show that suicides increased after March or around the recent Aug. 29 anniversary, Kessler said. Anniversaries of traumatic events such as divorce or a child's death do increase the chances of suicide, but concern by public figures and a feeling of pulling together may counterbalance that.