BEIJING - China has published the calculation methods of the Gini coefficient reflecting social wealth gap, the National Bureau of Statistics (NBS) announced on Friday.

A new survey system was set up at the end of 2012 to unify the income index for 400,000 households in both urban and rural areas. Historical income data have been adjusted and recalculated, according to an article on the NBS website.

The reformed system has been drafted referring to international norms, wrote Wang Pingping, NBS resident survey office chief.

Internationally comparable, China's recently released Gini coefficient reflects the income trend during the past decade, Wang said.

The 2003-2012 Gini coefficient, reflecting the gap between the rich and poor, was released by the NBS on January 18. All the annual figures were much higher than the warning level set by the United Nations.

China's statistics department used to publish two indexes -- per capita disposable income of urban residents and that of rural residents -- to reflect income distribution.

The reason for not publishing the index in previous years is due to the inconsistency in the income index for both urban and rural residents, and the unclear classification of migrant workers impacted by the country's urban and rural dual structure, wrote Wang.

Wang said the NBS will make further amendments and publish the Gini coefficient and calculation measurements in accordance with the new system.