Inequality in wealth affects stock market returns. When the rich get richer, stock market returns go down. This happens because the rich tend to invest more in stocks than the poor. The study found that when the income share of top earners in the U.S. increases, stock market returns decrease in the following year. This relationship holds true even when considering other factors that usually predict stock market returns. The same pattern is seen in other countries as well, especially in economies that are less open to international investments.