With wealth inequality one of the most pressing issues facing China, the public has been clamoring for accurate figures outlining the extent of the problem. On the 18th of January this wish was granted, when the country's top statistics authority released the annual Gini coefficient for 2012, after 12 years of silence on the issue.

The figures released by the National Bureau of Statistics (NBS) showed that the Gini coefficient - which measures income disparity with a figure of zero representing totally equally distributed wealth and a figure of one representing wealth concentrated in a single person's hands - stood at 0.474 last year, which was down from 0.477 in 2011 after a peak of 0.491 in 2008, the bureau's chief Ma Jiantang said in a press conference that included data from previous years.

The fact that the figures were lower than the results from other institutes sparked a public outcry. However, both figures are well above the 0.4 warning level outlined by the UN.

In contrast to the NBS figures, the Institute for Social Science Surveys under Peking University published a Gini coefficient of 0.514 for 2009, the National Survey Research Center at Renmin University of China provided an index of 0.555 for the same year, while the Survey and Research Center for China Household Finance under the Chengdu-based Southwestern University of Finance and Economics rated it at 0.61 for 2010.

The NBS put the indices of 2009 and 2010 at 0.490 and 0.481 respectively.

Ma frankly admitted that the latest official coefficient is relatively high as it falls between 0.47 and 0.49, and said it highlights the urgency of accelerating the country's reforms to narrow the income gap.

Estimates too low or too high?

All the researchers contacted by the Global Times said the different versions of the Gini coefficient published in recent years, both official and from academic institutions alike, serve as more of a glimpse at survey results than a complete picture of how wealth is distributed in society.

Gan Li, the director of the research center that published an edition of the Gini coefficient under the Southwestern University of Finance and Economics, said currently it cannot be determined whether the official figure was underestimated, as the NBS has not yet published the raw data or details of how it analyzed it.

"No survey is without discrepancies, only by making public the raw data can those results be consolidated," Gan told the Global Times.

Wang Xiaolu, deputy director of the National Economic Research Institute under the China Reform Foundation, said the coefficient largely depends on how the sample data is selected. "What matters here is that the sample group is representative, but each has its own shortcomings," he said.

"The problem here is that it lacks samples from high-income earners in its pool," Wang noted. "Their unwillingness to cooperate and the sometimes inaccurate figures they provide may detract from its accuracy."

However, others point out that the NBS has much wider access to samples, meaning their Gini coefficients may be more accurate.

The quantity of samples held by the bureau - some 240,000 urban and rural households and 160,000 other agencies including enterprises scattered across the country - is far larger than any other database, reads a report co-authored by Li Shi, executive director of the China Institute for Income Distribution under Beijing Normal University and Yue Ximing, professor from the School of Finance under the Renmin University of China.

In contrast, the coefficient of the Renmin University of China covers 12,000 households from 31 provincial-level regions and the Southwestern University of Finance and Economics has 8,400 households from 25 regions.

The report also revealed that there were problems in data collection caused by increasingly diversified forms of "gray" or unrecorded income, and that the lack of data from high-income households continues to artificially lower the results of the figures. This is more than a mere challenge in data collection, even judicial authorities and the Central Commission for Discipline Inspection of the Communist Party of China are often unable to track these illegal sources of income.

Why now?

Despite this debate, the release of the Gini coefficients marks a step forward from previous brief dispatches that only included the average per capita disposable income of urban residents, which was calculated at 24,565 yuan ($3,947) in 2012, and the per capita net income of rural residents, which stood at 7,917 yuan in 2012.

The NBS has started to release the Gini coefficient as one scale by unifying both the urban and rural households as one group, in contrast to its previous policy of announcing two different indices for rural and urban areas by splitting the population into two groups.

The income gap between urban and rural residents is one significant factor blamed for the country's uneven wealth distribution. The income ratio between urban and rural households was 1.8 to 1 in the late 1970s but had rocketed to 3.1 to 1 in 2012.

"This gap contributes to 60 percent of the rise in China's Gini coefficient, and very few countries in the world have such a big gap to fill," Yang Yiyong, the director of the Research Institute of Social Development under the National Development and Reform Commission, said in an interview with the Global Times earlier. Yang attributes the big gap to the very low salaries of migrant workers.

Li Daokui, professor of the School of Economics and Management under Tsinghua University, said the decline seen in the coefficient in recent years was understandable. "Due to the rising incomes of migrant workers the gap is narrowing," he said.

On the other hand, Li Shi said it was hard to judge whether the coefficient was really decreasing if the high-income group was only included as a small portion.

A press officer from the NBS told the Global Times that since December 1, 400,000 households across the country had been put into the sample pool to provide raw data to the bureau. When asked why the bureau's release of the separate indices stopped during the past decade, the official declined to comment, instead saying it was a requirement of the central government.

Ma Jiantang said the resumption of the Gini coefficient was due to resolutions made during the Party congress to build a well-rounded, well-off society by 2020, and Gini coefficients are one of the monitoring methods by which this goal is fulfilled.