A former head of China's National Bureau of Statistics (NBS) has defended the country's official economic data against Western doubts on its credibility.

China says its economy expanded 6.9 percent year-on-year in 2015 despite leading indicators of economic activity, including rail freight volume and electricity use, falling significantly or barely advancing. Western journalists have questioned whether such a high GDP growth is possible given the other indicators.

"There are many barometers to measure GDP," said Ma Jiantang, now vice president of the Chinese Academy of Governance, at a news conference on Wednesday. "Indicators such as rail freight volume and electricity use no longer paint the whole picture."

The total rail freight volume declined 11.9 percent in 2015 on a year-on-year basis, to 3.36 billion tons, according to an announcement published by the National Development and Reform Commission, China's top economic planner, in January.

Meanwhile, overall electricity use in the nation reached 5.55 trillion kilowatt-hours in 2015, up just 0.5 percent compared with 2014, the National Energy Administration said in January, according to its official website.

Ma said the slowdown of these two indicators reflected industrial restructuring. Rail freight has dropped as coal production has been cut, while low electricity use also tallies with transition into a service-oriented economy, which is less reliant on power use.

Facing doubts about China's latest GDP figures, officials emphasized in January that the nation uses scientific calculation methods that conform to international statistical standards.

The GDP growth rate in 2015 was down about 0.4 percentage point from 2014 due to downward pressures on the global economy including declining trade and rising financial risks, according to the NBS.

Ma also said the 6.5 percent to 7 percent growth target set for 2016 was "reasonable" and took into consideration both domestic and global economic conditions.