Current trade statistics miss a vital part of the story of where production occurs in the globalised economy, the OECD and WTO said on Wednesday, adding that China's trade surplus with the United States was overstated by a quarter.

The Organisation for Economic Cooperation and Development and the World Trade Organization unveiled a new database that seeks to measure the value-added in trade.

With manufacturing highly dependant on imports of raw and intermediate materials, the OECD-WTO database sought to reveal where value was being added throughout global trade.

It found that measured by value-added that China's bilateral trade surplus with the United States was over $40 billion (25 percent) smaller in 2009, and 30 percent smaller in 2005.

It said this reflected value attributable to goods China imported from the United States and Asian suppliers that China processed and ultimately sent the United States.

The OECD-WTO initiative also found that services were greatly underestimated in traditional trade statistics.

While services account for about two-thirds of output in developed economies, traditional statistics put their share in trade at less than one quarter, while on a value-added basis it rises to over 50 percent of exports for countries such as the United States, Britain and Germany.

With production chains becoming increasingly globalised, the OECD and WTO cautioned that "traditional measures of trade..., alone, may lead to misguided to misguided decisions being taken" in trade policy.

"Blocking imports will damage a country own productivity growth and automatically damage its competitiveness," said OECD chief Angel Guria.

The OECD-WTO calculations showed for example that a third of the value of the cars that Germany's powerhouse car industry exports is generated in other countries.

"If Germany would say 'no imports', well, no export of cars!" said Guria.

WTO Director-General Pascal Lamy said "countries that export more and best are the countries that import more and best."