wrote that the results of a retrospective fertility survey "make the case for a total [death toll] much lower - perhaps ten million lower - than that proposed by Yang". In 2014, Mao Yushi, a Chinese economist and winner of the 2012 Milton Friedman Prize for Advancing Liberty, put the death toll at 36 million. In 2019, Liao Gailong (廖盖隆), former Vice Director of the History Research Unit of the CCP, reported 40 million "unnatural" deaths due to the famine. In 1994, Chen Yizi (陈一谘), a former senior Chinese official and a top advisor to former CCP General Secretary Zhao Ziyang, stated that 43 million people died due to the famine. Economist Carl Riskin wrote that "Chen Yizi's methods of estimation are unknown" because they are unpublished. In 2010, Frank Dikötter, Chair Professor of Humanities at the University of Hong Kong and the author of Mao's Great Famine, estimated that at least 45 million people died from starvation, overwork and state violence during the Great Leap Forward, claiming his findings to be based on access to recently opened local and provincial party archives. His study also stressed that state violence exacerbated the death toll. Dikötter claimed that at least 2.5 million of the victims were beaten or tortured to death. His approach to the documents, as well as his claim to be the first author to use them, however, have been questioned by some other scholars. Reviewing Mao's Great Famine, historian Cormac Ó Gráda wrote that "MGF is full of numbers but there are few tables and no graphs. [....] On page after page of MGF, numbers [...] are produced with no discussion of their reliability or provenance: all that seems to matter is that they are 'big'." Dikötter provides a graphic example of what happened to a family after one member was caught stealing some food: In 2015, Yu Xiguang (余习广), an independent Chinese historian and a former instructor at the Central Party School of the Chinese Communist Party, estimated that 55 million people died due to the famine. His conclusion was based on two decades of archival research. Due to the lack of food and incentive to marry at that time, according to China's official statistics, China's population in 1961 was about 658,590,000, some 14,580,000 lower than in 1959. The birth rate decreased from 2.922% (1958) to 2.086% (1960) and the death rate increased from 1.198% (1958) to