Mirror-image factors are wiping out quant alpha

Equity momentum and value strategies are cancelling each other out, buy-siders say

Extreme correlations between different groups of stocks are fouling up the returns of widely used quant strategies.

A clustering of stocks into market darlings and market duds reached its most extreme level in September since the financial crisis. That has turned common momentum strategies – which go long high-momentum stocks and short those with low momentum – into a wholehearted bet against another popular strategy: value.

These strategies are traditionally seen as negatively correlated and