stylistic:style_transfer, structural:expansion
Methods of estimating the death toll and sources of error

Some outlier estimates include 11 million by Utsa Patnaik, an Indian Marxist economist, 3.66 million by mathematician Sun Jingxian (孙经先) and 2.6–4 million by historian and political economist Yang Songlin (杨松林).

The number of famine deaths during the Great Leap Forward has been estimated with different methods. Banister, Coale, and Ashton et al. compare age cohorts from the 1953, 1964, and 1982 censuses, yearly birth and death records, and results of the 1982 1:1000 fertility survey. From these they calculate excess deaths above a death rate interpolated between pre- and post-Leap death rates. All involve corrections for perceived errors inherent in the different data sets. Peng uses reported deaths from the vital statistics of 14 provinces, adjusts 10% for under reporting, and expands the result to cover all of China assuming similar mortality rates in the other provinces. He uses 1956/57 death rates as the baseline death rate rather than an interpolation between pre- and post-GLF death rates.

Houser, Sands, and Xiao in their 2005 research study using "provincial-level demographic panel data and a Bayesian empirical approach in an effort to distinguish the relative importance of weather and national policy on China's great demographic disaster" conclude that "in aggregate, from 1959 to 1961 China suffered about 14.8 million excess deaths. Of those, about 69% (or 10.3 million) seem attributable to effects stemming from national policies."

Cao uses information from "local annals" to determine for each locality the expected population increase from normal births and deaths, the population increase due to migration, and the loss of population between 1958 and 1961. He then adds the three figures to determine the number of excess deaths during the period 1959–1961. Chang and Halliday use death rates determined by "Chinese demographers" for the years 1957–1963, subtract the average of the pre-and post-Leap death rates (1957, 1962, and 1963) from the death rates of each of the years 1958–1961, and multiply each yearly excess death rate by the year's population to determine excess deaths.

Chen was part of a large investigation by the System Reform Institute think tank which "visited every province and examined internal Party documents and records."

Becker, Rummel, Dikötter, and Yang each compare several earlier estimates. Becker considers Banister's estimate of 30 million excess deaths to be "the most reliable estimate we have". Rummel initially took Coale's 27 million as a "most likely figure", then accepted the later estimate of 38 million by Chang and Halliday after it was published. Dikötter judged Chen's estimate of 43 to 46 million to be "in all likelihood a reliable estimate". He also claimed that at least 2.5 million of these deaths were caused by beatings, tortures, or summary executions. On the other hand, Daniel Vukovich asserts that this claim is coming from a problematic and unverified reference, because Chen simply threw that number as an "estimate" during an interview and because Chen hasn't published any scholarly work on the subject. Yang takes Cao's, Wang Weizhi's, and Jin Hui's estimates ranging from 32.5 to 35 million excess deaths for the period 1959–1961, adds his own estimates for 1958 (0.42 million) and 1962 (2.23 million) "based on official figures reported by the provinces" to get 35 to 37 million, and chooses 36 million as a number that "approaches the reality but is still too low".

Estimates contain several sources of error. National census data was not accurate and even the total population of China at the time was not known to within 50 to 100 million people. The statistical reporting system had been taken over by party cadre from statisticians in 1957, making political considerations more important than accuracy and resulting in a complete breakdown in the statistical reporting system. Population figures were routinely inflated at the local level, often in order to obtain increased rations of goods. During the Cultural Revolution, a great deal of the material in the State Statistical Bureau was burned.

According to Jasper Becker, under-reporting of deaths was also a problem. The death registration system, which was inadequate before the famine, was completely overwhelmed by the large number of deaths during the famine. In addition, he claims that many deaths went unreported so that family members of the deceased could continue to draw the deceased's food ration and that counting the number of children who both were born and died between the 1953 and 1964 censuses is problematic. However, Ashton, et al. believe that because the reported number of births during the GLF seems accurate, the reported number of deaths should be accurate as well. Massive internal migration made both population counts and registering deaths problematic, though Yang believes the degree of unofficial internal migration was small and Cao's estimate takes internal migration into account.

Coale's, Banister's, Ashton et al.'s, and Peng's figures all include adjustments for demographic reporting errors, though Dikötter, in his book Mao's Great Famine, argues that their results, as well as Chang and Halliday's, Yang's, and Cao's, are still underestimates. The System Reform Institute's (Chen's) estimate has not been published and therefore it cannot be verified.