Between 170,000 and 255,000 people have died in Sudan's war-torn Darfur region since 2003, according to a new study that says the death toll is often under reported. But the actual number of people who have died could be as high as 400,000, said one of the study's author's John Hagan, a sociology and law professor at Northwestern University in Illinois. There is much uncertainty in estimating the death toll in Darfur because of difficulties getting accurate body counts, according to the study, which was published Friday in the journal Science. "The core of the problem is that in natural disasters, you can count the bodies or relatives are relatively accessible" to talk to, Hagan said in a telephone interview Friday. "This just isn't happening in Africa. There are mass graves, but NGOs (non-governmental organizations) don't have access to them." The conflict in Darfur began in early 2003 when ethnic African tribes revolted against the Khartoum government. The Arab-dominated Sudanese government has been accused of unleashing Arab militiamen known as janjaweed who have been blamed for widespread atrocities, including rapes and killings. Hagan said some news agencies and other organizations have been under-reporting the death toll as tens of thousands and other death toll figures were not accurately compiled. UN officials have given death toll estimates of 180,000 to 200,000, while the US State Department issued a report in spring 2005 that estimated between 63,000 and 146,000 had died. In their study, the authors used World Health Organization and Doctors Without Borders surveys done in refugee camps in West Darfur to obtain monthly mortality rate estimates. They used a ratio of the mortality rates to number of displaced people in the camps to extrapolate the data to cover the entire Darfur region over 31 months. "We tried to sort out the problems of overestimation and underestimation," of the death toll, Hagan said, adding that the study was the first time research on the death toll in Darfur had appeared in a peer-reviewed scientific publication. "We can say safely and cautiously that the toll is over 200,000," he said. But, Hagan said, the study had limitations, and the number is likely to be much higher, even reaching 400,000. The study covers 31 months beginning in the fall 2003 and ending in the spring of this year. The research does not include the months since then and the months when the conflict first began in early 2003, he said. The study also does not include missing people who are presumed dead, Hagan said. Rich Brennan, the director of the New York-based International Rescue Committee's health unit, said he thinks the study's estimate is correct but believes some of the research methods used were flawed. "I think the estimate is reasonable, but I don't think the research used appropriate methodologies to reach that conclusion," said Brennan, who said the study did not include all possible surveys done in Darfur. But Brennan said the international community should be less concerned about the exact number of people who have died and place more emphasis on the crisis itself. "It's a tragedy and a travesty regardless of the numbers. I think it doesn't make it much worse a humanitarian crisis whether its 200,000 or 300,000, it's still an absolute crisis," he said.