Stock investors have been watching the runup in US Treasury yields with considerable alarm of late. The widening premium of the 10-year yield over the earnings yield on the S&P 500 Index has garnered particular attention. It’s not supposed to be this way after all. Treasuries are broadly considered the world’s safest investment, whereas stocks are among the riskiest. Earnings yields are, therefore, normally higher than Treasury yields — what finance wonks call an equity risk premium.

But the equity risk premium turned negative late last year for the first time in more than two decades. The earnings yield, which is simply the inverse of the better-known price-earnings ratio, dipped down to 3.9% in November, based on Wall Street analysts’ consensus estimates for companies’ current fiscal year. Meanwhile, the 10-year Treasury yield drifted up to 4.4% and is now closer to 4.7%, while the S&P 500’s earnings yield hangs around 4%.