As an economist who works with large amounts of Chinese data this issue has arisen many many times without a satisfactory solution. The Economist discusses this issue at length. I tend to use province level data - this raises a set of problems that this article also covers.
An aberrant abacus
AS CHINA'S importance in the global economy increases, investors are paying more attention to its economic numbers. Yet the country's official statistics are notoriously ropy. Some commentators accuse China's government of overstating GDP growth for political reasons, others complain that the official inflation rate is fraudulently low. So which data can you trust?
One reason to be suspicious of GDP figures is that China is always one of the first countries to report them, usually only two weeks after the end of each quarter. Most developed economies take between four and six weeks to produce them.
So which data to trust. From Statistics that Don’t Add Up [China Business Services]
The Economist also provides a guide (developed by Goldman Sachs) to the reliability of official Chinese numbers. It gives a score to different sets of stats, 5 being the most reliable, and 0 the least:
• Foreign Trade: 5
• Money Supply: 5
• Industrial production: 4
• Consumer Prices: 4
• GDP: 3
• Retail Sales: 3
• Fixed Investment: 2
• Employment: 2
• Average Earnings: 1
• Unemployment: 1
On the issue of province versus country level data:
Chinese provinces independently report GDP, and a weighted average of their figures consistently gives higher rates of output and growth than those reported by the central government (see chart). True, local officials have an incentive to inflate growth numbers because promotion depends upon economic performance; however, experience suggests that number crunchers in local government are more accurate than Beijing's. For instance, the figures first published for 2004 showed that the sum of the provincial GDPs was 19% bigger than the reported national figure. Lo and behold, in 2005, after a national economic census picked up more services, the NBS revised its GDP up by 17%; it also lifted the annual growth rate over the previous decade.
Finally, as someone who uses a lot of trade data here is the good news:
Foreign trade is perhaps the most accurate economic indicator. Critics accuse China of fiddling its trade figures, because the value of its exports as measured by the importing country is always much bigger than what the Chinese report. This discrepancy reflects the fact that China's bilateral trade figures exclude goods shipped to Hong Kong before being re-exported. But this should not affect total export figures and detailed Hong Kong data are available to adjust bilateral trade flows.
An interesting topic.