https://www.sciencedirect.com/science/article/pii/S0304405X9...
Ray Dalio has written a few articles about the strategy used by his "All Weather" hedge fund, a summary is here
https://www.bridgewater.com/research-and-insights/the-all-we...
Now he won't tell you how "Pure Alpha" works because if he did he'd have to kill you.