Last October, Jaffray Woodriff, founder, chief executive and portfolio manager of Quantitative Investment Management, a $3.2bn (€2.4bn) hedge fund, was on the verge of interrupting his computer-generated models and pulling out of his positions.

Woodriff's models and analysis, which are automated, were all saying the same thing: that the correlations in financial markets could not last forever and that trading opportunities - which the computer had studied, compared, back-tested, stress-tested and simulated every which way - would turn around. "I was very scared in October about the global economy, but I knew I wasn't really going to intervene with our systems," he said.