But central Banks already try to estimate the "output gap", the extent to which economic growth is above or below trend, when setting interest rates-and that's fiendishly difficult.

Rather than follow the conventional route of deriving an inflation forecast from an estimate of potential output, they do the opposite: they infer the output gap from the behaviour of inflation.

When someone see a mature man with a woman half his age, they estimate him to be much older than it really is because of the obvious gap, said the study.