He is worth around $25 billion, the founder and majority owner of Renaissance Technologies, possibly one of the most successful investment management firms ever.

But it seems that even Jim Simons sometimes has doubts about the quantitative machine learning models and processes that underpin his wealth, not least his holdings in the Medallion Fund, which has generated gross annualised returns of around 66 percent since 1988.  

This was especially the case in late December 2018. The S&P 500 had fallen by 10 percent during the month, the worst December performance in history.

Rather than relying on Renai...