Dr David Rush, a professor and epidemiologist at Tufts University in Boston, said: "Over the last 25 years, this sort of methodology has been used more and more often, especially by relief agencies in times of emergency."
The study, published earlier this month by the Lancet medical journal, employed a method known as "cluster sampling" in which data are collected through interviews with randomly selected households.
Critics, including President George Bush, have said the results are not credible, but Rush said traditional methods for determining death rates, such as counting bodies, are highly inaccurate for civilian populations in times of war.
Researchers from Johns Hopkins University in Baltimore and al-Mustansiriya University in Baghdad estimated with 95 per cent certainty that the war and its aftermath have resulted in the deaths of between 426,000 and 794,000 Iraqis.
Other estimates have calculated the number of extra Iraqi deaths to be much lower. The Iraq Body Count Database calculates that between 43,850 and 48,693 extra civilians have died since the invasion.
Rush, speaking at a meeting in Los Angeles on the medical consequences of the Iraq war, said that the relatively small size of the sample - 1,849 households - does not change the findings, although it does widen the "confidence limits," hence the large range of the estimated additional deaths.
A Lancet report puts the average
daily death toll in the hundreds
In addition, the biases inherent in cluster sampling, such as wording of questionnaires, would tend to undercount, rather than inflate, the number of deaths, Rush said.
Michael Intriligator, professor of economics at the University of California at Los Angeles, also backed the finding.
"I think this is an extremely credible study," he said.
Rising death rate
Intriligator, who said he commonly uses cluster sampling in his own work, noted that the study's most remarkable finding was that the death rates in the country have risen from 5.5 per thousand Iraqis per year before the invasion to 13.2 per thousand per year as of the study's July cutoff.
In addition to violence, death rates in Iraq are on the rise because of threats to public health, including poorly equipped hospitals, said activist Dr Dahlia Wasfi.
Jonathan Parfrey, executive director of the Los Angeles chapter of Physicians for Social Responsibility, said: "The affects on the civilian population of the war in Iraq have been grossly underestimated."