BEIJING (Reuters) - China will unify the way it calculates provincial economic output to help close a gap with national figures, the country's chief statistician said on Tuesday, amid skepticism about the reliability of Chinese data.

The difference between gross domestic product reported in aggregate by China's 31 provinces in 2011 and the national level, for instance, showed a huge discrepancy, roughly equivalent to the GDP of Turkey.

"We will promote statistical reform and innovation this year to actively and steadily push forward unified accounting for regional GDP," said Ma Jiantang, head of the National Bureau of Statistics.

The bureau would draw up plans for introducing the unified statistical standards on local GDP this year, as it conducts the latest economic census, Ma said in remarks published on the central government website, www.gov.cn.

The bureau would revise national and local GDP data for 2013 and prior years to make them consistent and strictly calculate national and local GDP and growth rates for each quarter this year, Ma said without elaborating.

The combined economic output of China's provinces has long exceeded that of the national level compiled by the bureau, raising suspicion that some growth-obsessed local officials have cooked the books.

Chinese leaders have recently set new standards for local officials, stressing that their performance cannot be simply based on regional growth rates, but should include resource and environmental costs, debt levels and work safety.

(Reporting by Kevin Yao; Editing by Nick Macfie)