As the late John Kenneth Galbraith remarked: “The only function of economic forecasting is to make astrology look respectable.”

But that does not mean we can say nothing useful. One can at least identify economic trends and a few known unknowns.

The world economy is extremely likely to grow. It has, after all, grown every year since the second world war, with the sole exception of 2009, the year of the global financial crisis, when it shrank 2 per cent at market exchange rates and remained roughly constant at purchasing power parity. The International Monetary Fund believes the world economy will grow at nearly 4 per cent, at PPP. This is a good starting point. It is also a remarkable one: at 4 per cent annual growth, the world economy doubles every 18 years.