Take a look at some fascinating data compiled by the Commerce Department, and quietly released last year. This shows that in the past few years, the number of American jobs supported by exports has risen as overseas sales have grown. In 2009, exports created 9.7m jobs; by 2013 the tally was 11.3m.

This is cheering. And since overseas sales rose further in 2014, amid a wider economic recovery, there is every reason to think that when the commerce department publishes the 2014 tally the number of export-linked jobs will have grown again.

But there is a billion dollar catch. Look at how many jobs are being generated per dollar of sales and the graph steadily slopes down. Back in 2009, each billion dollar’s worth of exports was creating 6,763 jobs. In 2013, it was 5,590 jobs. That is a fall of 17 per cent — in just four years.

There are two ways to interpret this trend. If members of Congress want to feel cheery at the start of a new year, they could celebrate the fact that American companies are becoming more innovative and competitive on the world stage. This partly reflects lower energy costs. But another factor is that as recovery has taken hold in the US, levels of automation and digitisation are rising sharply too.

That is prompting more US companies to develop production inside America, since it holds down labour costs. While Chinese workers might be cheaper than their American counterparts, robots are more cost effective than both — and often more competent.

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