Economic forecasts of the trend in interest rates, the future of the euro or next year's GNP for Vanuatu are very often wrong. But then economic forecasting is more difficult than predicting weather.
The computer models have to describe the expected emotional and thinking behaviour of human beings, as distinct from an inanimate, albeit ever-fickle, atmosphere.
Economists must distil their theories about people into equations that encapsulate a myriad of variables, and as in meteorology, their forecasts will not work if the basic model is inadequate, or if input data are untimely. There are times when economists, like meteorologists, go down cul-de-sacs. The case in point was a theory which attempted to link the economic well-being of the US, via alleged cycles in the weather, to the motions of the moon.
This lunacy, in its literal sense, began with "Kuznets's swings". Simon Kuznets was an American economist who suggested in the early 1930s that the US economy was subject to regular cycles of about 20 years duration.
Throughout each cycle, he maintained, agricultural and industrial production, financial investment and various demographic indicators could be seen to rise and fall in a pattern which repeated about every 20 years.
Half a century later another economist blew the dust from Kuznets's theories, and recalled from his interest in astronomy that the moon exerts a tidal influence on our atmosphere.
As the Earth revolves, the moon produces a small twice-daily rise and fall in barometric pressure. Because of peculiarities in the moon's orbit, this tidal effect varies in magnitude over the decades, one component of the variation having a cycle of 18.613 years. Twenty, this economist opined, was not too far from 18.613; was it possible that the moon had something to do with Kuznets's swings?
His next step was to connect the 18-year lunar cycle to the weather, which he did to his own satisfaction by relating it to US rainfall figures. He found, he said, a corresponding cycle in the rainfall, with wet years in 1917, 1936, 1954, and 1973, all coinciding with times of maximum lunar tidal force.
It was then easy to relate this information to the US grain supply which, not surprisingly, showed excellent yields in the years when rain was plentiful.
The final step was to postulate that variations in the crop production must ripple through the largely agrarian economy of the US, thus tracing to the moon the apparent "swings" that had been recognised by Kuznets.