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 slightly fewer than 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. According to a 2001 academic source, the most widely accepted estimates of excess deaths under the Khmer Rouge range from 1.5 million to 2 million, although figures as low as 1 million and as high as 3 million have been cited; conventionally accepted estimates of deaths due to Khmer Rouge executions range from 500,000 to 1 million, "a third to one half of excess mortality during the period". However, a 2013 academic source (citing research from 2009) indicates that execution may have accounted for as much as 60% of the total, with 23,745 mass graves containing approximately 1.3 million suspected victims of execution.