BEIJING, Jan. 20 -- Claims that China has overtaken the United States as the world's largest economy were denied by the head of China's National Bureau of Statistics (NBS) on Tuesday.

"The NBS does not countenance these claims by some scholars and media organizations," said bureau head Ma Jiantang at a press conference in Beijing.

A study last year by the International Comparison Program (ICP) projected that China would overtake the U.S. in 2014 based on purchasing power parity (PPP), which measures GDP in terms of prices of the same goods between nations. PPP takes into account the purchasing power of a currency rather than market exchange rates. Roughly, how many family cars, Big Mac's, units of electricity or university educations can one person's salary buy in one nation, as opposed to another person's salary in a different country.

"The NBS also took part in the study, which established PPP for different countries, but we need to be cautious in applying the study results," Ma said.

"For various reasons, we think the PPP methodology might have underestimated actual price levels in China and over-estimated China's GDP. With that proviso, we don't agree with the results," Ma said.

Despite a continuously growing economy, it should be noted that China remains a developing country with a population of 1.3 billion, which means per capita GDP is still very low.

Latest data released by the NBS showed the Chinese economy expanded 7.4 percent year on year to 63.65 trillion yuan (10.4 trillion U.S. dollars) in 2014.