A new scientific study estimates that as many as 100,000 Iraqi civilians died in the US-led invasion and its aftermath. The study, reported in a respected international medical journal, says most of the casualties came from aerial bombardment.

In an article in the online edition of the British medical journal The Lancet, U.S. and Iraqi researchers calculate that around 100,000 Iraqi civilians have died since the U.S.-led invasion in March of 2003.

Dr. Gilbert Burnham of the Johns Hopkins School of Public Health, a co-author of the study, says most of the casualties were women and children.

"We shouldn't really fix on the numbers," he said. "We should fix on the fact that, you know, these are civilians, predominantly women and children, that are getting caught up in an urban conflict and they're carrying the brunt of the consequences."

The report, conducted jointly by researchers from Johns Hopkins University, Colombia University, and Al-Mustansiriya University in Baghdad, is the first attempt to scientifically calculate civilian casualties of the Iraq war. Previous non-governmental estimates range anywhere from 10,000-30,000. The U.S. government has said it does not calculate civilian casualties in Iraq.

Asked to comment on the study, a Defense Department spokesman said that there is no accurate way to validate the estimates of civilian casualties by this or any other organization. He added the Iraq war was prosecuted in the most precise fashion of any conflict in the history of modern warfare and that multinational and Iraqi security forces work painstakingly to avoid civilian casualties.

The researchers conducted the survey much like a public opinion poll, surveying a scientifically selected random sample of households about deaths suffered in the family. They visited nearly 1000 homes in 33 neighborhoods across the country.

The scientists involved in the report acknowledge that the data on which they based their estimates were of "limited precision," because the quality of the information rests on the accuracy of the household interviews conducted for the study. The interviewers were Iraqi, most of them doctors.

However, Dr. Burnham says, results from Fallujah were omitted. He said casualties there were so great that including the results from Fallujah would have made the sample unrepresentative.

The single biggest cause of violent death in Iraq since March, 2003, Dr. Burnham says, was aerial bombardment.

"Almost all of these excess deaths related to conflict were related to aerial bombardments of some sort - armaments that fell out of the sky, as it were," he said. "And some people said they were helicopters, some said they were bombs, some said they were rockets. But we just classified these as aerial attacks in some way."

Dr. Burnham says similar studies of previous conflicts show that most civilians die not from bombs or bullets, but from being cut off from medical care. But what they found in Iraq, he says, appeared to be very different.

"Usually in warfare or conflict situations, deaths occur because of poor access for health care, or, like in the Balkans, one couldn't get to dialysis units or get their insulin and so forth," Dr. Burnham explained. "So the finding that almost all these excess deaths were due to actual violence was a bit of a surprise."

Dr. Burnham says the study found no evidence of civilian deaths from improper conduct by U.S. troops or other coalition forces. The researchers urge more study be done on the issue to clarify their findings.