An investment approach that profits from the divergent paths of high- and low- momentum stocks over time, a strategy that had one of its biggest gains on record in 2015, seized up in the last three months, posting the worst quarter in six years. The plunge helped zap returns among a big category of quantitative hedge funds, the so-called market neutral group, whose year-to-date decline of 2.3 per cent is the largest since 2012.