Since the global economic crisis, sharp divergences in economic performance have contributed to considerable stock-market volatility. Now, equity prices are reaching relatively high levels by conventional measures – and investors are starting to get nervous.
The question is whether stock valuations are excessive relative to future earnings potential. The answer depends on two key variables: the discount rate and future earnings growth. A lower discount rate and/or a higher rate of expected earnings growth would justify higher equity valuations.
The S&P’s price-to-earnings (P/E) ratio for the trailing 12 months is close to 20, compared to a long-run mean of 15.53 and a median of 14.57. The Shiller P/E ratio – based on average real (inflation-adjusted) earnings from the last ten years – is at 27.08, with a mean and median of 16.59 and 15.96, respectively. And, in February, the forward 12-month earnings P/E ratio, which uses managers’ future earnings guidance, reached an 11-year high of 17.1, with the five- and ten-year averages standing at about 14- and the 15-year average at 16.
The stock market’s recent performance often is attributed to the unconventional monetary policies that many central banks have been pursuing. These policies, by design, lowered the return on sovereign bonds, forcing investors to seek yield in markets for higher-risk assets like equities, lower-rated bonds and foreign securities.
According to the standard formulation, stock prices tend to revert toward the present value of estimated future earnings (including growth in those earnings), discounted at the so-called “risk-free rate,” augmented by an equity risk premium. More precisely, the forward earnings yield – that is, the inverse of the P/E ratio – is equal to the risk-free rate plus the equity premium, minus the growth rate of earnings. (Of course, markets take detours along the way, driven by, say, irrational exuberance, temporary declines in the impact of value investors, or mistimed contrarian trades.)
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