Over the long term, the correlation of the S&P 500 Index to long-term (20-year) Treasuries has been close to zero—over the period 1927-2021, the monthly correlation was just 0.063. However, as Lieven Baele and Frederiek Van Holle, authors of the 2017 study Stock-Bond Correlations, Macroeconomic Regimes and Monetary Policy, noted: “There have been persistent episodes of large negative stock-bond correlations, in particular since the end of the 1990s.