The stock market has been in a new price regime for 20 years

Almost every stock market forecaster will agree that stock prices look expensive when considered relative to earnings (P/E). Indeed, this is one of the main reasons why Wall Street strategists aren’t very bullish about the second half of 2017.

However, in two recent letters to investors, GMO’s Jeremy Grantham questions the way we often look at P/E ratios to think about the stock market. Specifically, he suggests the stock market may be — at least temporarily — in a “new normal” of elevated P/Es.

The P/E, or price/earnings, ratio is the most popular and most straightforward way of measuring value in the stock market. For the S&P 500 (^GSPC), it’s calculated by taking the index level (P) and dividing it by earnings per share (E). There are several ways to calculate this: You can use trailing 12-month earnings or the forecast for next-12-month earnings; you can use GAAP earnings or non-GAAP earnings; you can use one year’s worth of earnings or you can use the average of 10 years worth of earnings.

Analysts and investors draw the same conclusion from the P/E: If it is above some long-term average, then stocks are expensive. And vice versa.

As we begin the second half of 2017, it’s worth revisiting what Grantham has said.

What if the average P/E we’re all using is wrong?

Grantham considers the last 20 years of stock market behavior and observes that things aren’t what they used to be.

“For a long and painful 20 years – for someone betting on a steady, unchanging world order – the P/E ratio stayed high by 1935-1995 standards,” Grantham wrote in May. “It still oscillated the same as before, but was now around a much higher mean, 65% to 70% higher! This is not a trivial difference to investors, and 20 years is long enough to test the apocryphal but suitable Keynesian quote that the market can stay irrational longer than the investor can stay solvent.”

“Old normal” valuations versus “new normal” valuations.
“Old normal” valuations versus “new normal” valuations.

The issue is not so much that average valuations seem elevated. Rather, it’s that traumatic market events haven’t jolted valuations back to the more historic levels.

“After the bursting of the tech bubble, the failure of the market in 2002 to go below trend even for a minute should have whispered that something was different,” Grantham said. “Although I noted the point at the time, I missed the full significance. Even in 2009, with the whole commercial world wobbling, the market went below trend for only six months. So, we have actually spent all of six months cumulatively below trend in the last 25 years! The behavior of the S&P 500 in 2002 might have been whispering in my ear, but surely this is now a shout? The market has been acting as if it is oscillating normally enough but around a much higher average P/E.”