Economic forecasting is not a science. Indeed, its critics are sometimes more scathing and put it on a par with astrology. Last week, some figures were published that required economists to practise their black arts with the greatest skill. In the UK, GDP in the first quarter was shown to have grown by only 0.3pc, well down from growth in the previous year and well below expectations.

On its own, this might be nothing to write home about. After all, macro-economic data is notoriously unreliable and the GDP figures are frequently revised – usually upwards.

Nevertheless, it was striking that the first quarter was also shown to be pretty weak in the United States, with growth also well down from previous quarterly figures and below expectations.

Moreover, economic reports from China, and for much of South East Asia, continue to be on the weak side – although Japanese data have been mixed. Meanwhile, the Russian economy is set to contract this year by 5pc, and in Brazil the economy has ground to a halt.

Ironically, the only bit of the world economy which seems to be a bit perkier is the eurozone, where Q1 growth looks like coming in at about 0.4pc, for once putting it ahead of growth in the US and the UK. Mind you, even in the eurozone things aren’t exactly set fair. Figures from the beginning of the second quarter have been on the soft side, suggesting that there, too, the economy may be succumbing to the slowdown.

What on earth is going on? It may well be that there are umpteen different factors making for slower growth in different parts of the world. Yet it is always intellectually unsatisfying to rely on a series of ad hoc explanations. We should look for some common factor that unites, if not all the evidence, then at least a good part of it. Is there such a thing?

There is one good candidate – lower oil prices. If this is the reason for weaker growth, it would be surprising, to put it mildly. You could argue that lower oil prices should make no overall difference to the economy. In the jargon, they are a zero-sum game. In fact, most economists, including yours truly, have argued that lower oil prices should give a major boost to the world economy because oil consumers have a greater propensity to spend their income than oil producers.

David Fuller's view

In addition to “oil consumers have a greater propensity to spend their income than oil producers”, I would add that lower oil prices will also improve confidence among all who consume this commodity in its various forms.  My guess is that we will see evidence of this in the second half of this year. 

Moreover, accommodative monetary policies, cheaper oil prices and generally less expensive food combine to provide a stimulus to economic recovery.  This will help to reduce the negative deflation caused by six years of deleveraging by individuals and corporations, which also reduced government tax revenues. 

Judging from Roger Bootle’s last paragraph in his full article, he is expecting a Conservative victory on Thursday. 

(See also - Letters: The universal message after May 7 has to be that Britain is open for business)