It is difficult to feel sorry for analysts at the best of times, but those analysts covering the investment banking industry come closest to deserving sympathy for struggling to predict performance in such a volatile industry.

In a well-rehearsed dance, analysts covering banks such as Goldman Sachs and Morgan Stanley, or the investment banking arms of Deutsche Bank or UBS, set optimistic targets months in advance, only to slash them radically in the few weeks before earnings are announced. They are then still made to look foolish as the banks conveniently beat these lowered expectations. Goldman Sachs, for example, has beaten forecasts in 18 of the past 20 quarters.