Ben Kiernan estimates that 1.671 million to 1.871 million Cambodians died as a result of Khmer Rouge policy, or between 21% and 24% of Cambodia's 1975 population. A study by French demographer Marek Sliwinski calculated nearly 2 million unnatural deaths under the Khmer Rouge out of a 1975 Cambodian population of 7.8 million; 33.5% of Cambodian men died under the Khmer Rouge compared to 15.7% of Cambodian women. Researcher Craig Etcheson of the Documentation Center of Cambodia (DC-Cam) suggests that the death toll was between 2 million and 2.5 million, with a "most likely" figure of 2.2 million. After five years of researching mass grave sites, he estimated that they contained 1.38 million suspected victims of execution. Although considerably higher than earlier and more widely accepted estimates of Khmer Rouge executions, Etcheson argues that these numbers are plausible, given the nature of the mass grave and DC-Cam's methods, which are more likely to produce an under-count of bodies rather than an over-estimate. Demographer Patrick Heuveline estimated that between 1.17 million and 3.42 million Cambodians died unnatural deaths between 1970 and 1979, with between 150,000 and 300,000 of those deaths occurring during the civil war. Heuveline's central estimate is 2.52 million excess deaths, of which 1.4 million were the direct result of violence.