China posted its slowest growth in a quarter century in 2015, official data showed Tuesday, confirming a loss of momentum in the world’s second-largest economy that continues to chill global activity and spook markets world-wide. As WSJ's Grace Zhu reports:

China’s gross domestic product expanded by 6.9% year-over-year in 2015, down from the 7.3% gain reported in 2014, data from the National Bureau of Statistics showed. The figure was in line with a median 6.9% increase forecast by 15 economists polled by The Wall Street Journal. The statistics bureau also said Chinese economy expanded 6.8% on year in the fourth quarter,...