The first quarter of 2019 ended on Friday with a gain in the Standard & Poor's 500 stock index of 13%, the best quarterly performance since the third quarter of 2009.

Publicly traded shares of large American companies, in decades past, averaged about a 10% total return per year. So, a double-digit gain in a three-month period is extraordinary by historical standards.

The strong performance in stocks occurred despite a long list of worries, including: inversion of the yield curve, a bad sign that has preceded every recession in post-War U.S. a U.S. trade war with China, the world's second-largest economic power signs of a sharp slowdown across Europe and in China lower earnings growth forecasts by Wall Street analysts for S&P 500 companies for 2019