Over the past 30 years, the US grown at an annual average rate of 2.4 per cent, and China by 9.3 per cent. 

But a paper in the latest issue of the world-class Journal of Economic Perspectives argues persuasively that the sustainable Chinese growth rate in the medium and longer term is much lower, in the range of 3-4 per cent a year.

Hongbin Li and colleagues, based both in Stanford and top universities in China, note that growth in China since the start of the economic reforms in 1978 has been the fastest that any large country has sustained for such a long period of time. But much of this is due to the rapid transition from a centrally planned to a market oriented economy. Forty years ago, virtually no-one operated in the private sector. Now, well over 80 per cent of workers are in the private sector. This shift obviously cannot be repeated.

Closely intermingled with this has been the massive move of population from the countryside to the cities. More precisely, from low productivity agriculture to higher productivity urban economic activities. But the annual growth rate of rural-to-urban migration has declined from over 11 percent in the 15 years before 2000 to only 3 percent since then. And the growth of migration almost certainly will fall further given that rural-based surveys are finding that less than 10 percent of young able-bodied rural individuals are now living (and working on farms) in rural areas.

Until 2011, the authors point out that China enjoyed what they call a “demographic dividend”. The age group of the working population was unusually high as a share of the population as a whole. But because of what the authors tactfully refer to as “the fall in fertility” since the early 1980s, this is now declining fast. The one child policy was mainly responsible, but higher incomes also reduce birth rates.

China remains a huge and growing economy. But projections that it will overtake the US within readers’ lifetimes seem fanciful.