As the world awaits China's third-quarter gross domestic product (GDP) figures on Monday, the accuracy of mainland data is once again up for debate.

A growing section of financial market participants and journalists has speculated that recent numbers might be painting a more flattering picture of the world's second largest economy than is the reality.

But according to research, China's economy is likely much bigger than official data suggest.

In a report published by research institution Center for Strategic and International Studies (CSIS) last month, Daniel Rosen and Beibei Bao showed that 2008 GDP was actually 13-16 percent larger than official figures, while 2013 GDP stood at $10.5 trillion rather than the official $9.5 trillion.

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What might explain this mismatch? The authors think the difference could be explained by how China calculates, or does not calculate, economic activity.

China currently measures GDP using the United Nations System of National Accounts standards set in 1993, which has a narrower coverage of services sector, while the bulk of developed nations use the latest standards set in 2008.