Old-fashioned stock-pickers have staged a comeback in fund management this year, but it may have come too late to win back the world's biggest investors, who are increasingly picking apart what these managers do — and finding a way to do it more cheaply.

The approach these investors are taking is known as "factor investing", which breaks down the elements of a security or investment strategy to identify what is driving its performance. While the idea has been around for several years, it is going increasingly mainstream among the world's largest pension funds, sovereign wealth investors, insurers and private banks, according to asset manager Invesco.