Oct. 11 (Bloomberg) -- More than 600,000 people have died violent deaths in Iraq since the U.S.-led invasion in March 2003, according to a study released today by the Johns Hopkins Bloomberg School of Public Health and Al Mustansiriya University in Baghdad.

Gunshots were the most common cause of death, with males ages 15 to 44 accounting for 59 percent of the total as of July 2006, the study said. The estimates were made after a nationwide survey of 1,849 Iraqi households between May and July 2006.

President George W. Bush dismissed the findings even as he acknowledged that ``the brutality of Iraq's enemies has been on full display in recent days.''

``I don't consider it a credible report; neither does General Casey and neither do Iraqi officials,'' Bush said when asked about the study at a White House news conference. The study's methodology is ``pretty well discredited,'' he said.

The estimate of violent deaths -- 601,027 -- exceeds what other groups have found over a similar period, including Iraq Body Count, a London-based group that opposes the war and compiles its casualty toll from English-language media reports and official statements. The group estimates that between 43,491 and 48,283 died up to Sept. 26.

Iraq Body Count spokesman Hamit Dardagan said the group wouldn't comment on this new study ``until we have read and digested the full report.''

`Precise Number' Not Goal

Gilbert Burnham, lead author of the study, said the researchers' intent wasn't ``to try to find a precise number.''

``If it turns out that we were able to do a much bigger study and we found that the death rate was 580,000 that would be essentially the same magnitude as what we're turning up here,'' Burnham said on a conference call with reporters today.

Burnham is co-director of the Center for Refugee and Disaster Response at the Bloomberg School, which is named for Michael Bloomberg, founder and major shareholder Bloomberg LP, which owns Bloomberg News.

Burnham and the other authors of the study, which is published in today's online edition of The Lancet, a scientific journal, relied on a population-based method to collect information, asking members of each household for the number of births and deaths that occurred there over a specified time.

Approximately 1,474 births and 629 deaths were reported among the 12,801 people surveyed in 47 randomly selected areas. Those numbers were multiplied to represent the nation's total population of 26.1 million.

Killers Unknown

Almost half of those surveyed didn't know who killed their respective household member. Information on whether the victim was involved in armed combat, terrorism, or criminal activity wasn't collected.

Including those who died from natural causes, the number of deaths overall was 654,965, which represents about 2.5 percent of the Iraqi population, according to the study.

Burnham said the study's ``confidence interval,'' the range in which researchers are 95 percent sure ``the true answer lies,'' is from 392,000 to 942,000.

The authors acknowledged that ``extreme insecurity'' in the regions surveyed restricted the size of survey teams, the number of supervisors and how much time could be spent in each location. Family members might also have misreported deaths, and ``large-scale migration'' out of Iraq could have affected the estimates, the study said.

The same survey done in 2004 by Baltimore, Maryland-based Johns Hopkins and the Al Mustansiriya University estimated more 100,000 deaths from all causes, excluding Falluja households. Such survey methods were used to gauge mortality rates in the Congo, Kosovo, Sudanese conflicts.

There have been 2,745 U.S. military deaths since the U.S.- led invasion in March 2003, the U.S. Defense Department said yesterday.

To contact the reporter on this story: Nadine Elsibai in Washington at nelsibai@bloomberg.net.

Last Updated: October 11, 2006 14:20 EDT