What are we to make of the following graphs? Figure 1 presents the long historical view of the Price-to-Earnings ratio on the S&P500 Index. Figure 2 presents a similar view, adjusting the P/E ratio for the impact of inflation on earnings.
Standard Price/Earnings Ratio for the S&P500 Index (average of all companies)
Current S&P 500 PE Ratio: 19.04 -0.19 (-0.97%)
4:29 pm EDT, Tue Aug 5
Price to earnings ratio, based on trailing twelve month “as reported” earnings.
Current PE is estimated from latest reported earnings and current market price.
Source: Robert Shiller and his book Irrational Exuberance for historic S&P 500 PE Ratio.
Cyclically-Adjusted Price-Earnings Ratio for the S&P500 Companies
Current Shiller PE Ratio: 25.39 -0.25 (-0.97%)
4:29 pm EDT, Tue Aug 5
Shiller PE ratio for the S&P 500.
Price earnings ratio is based on average inflation-adjusted earnings from the previous 10 years, known as the Cyclically Adjusted PE Ratio (CAPE Ratio), Shiller PE Ratio, or PE 10 — FAQ.
Against these measures, stock prices today seem high. Looking over the last 130 years, you see big spikes in P/E ratios suggesting bubbles “irrational exuberance” in advance of capital market instability (1929 stock market crash, the Internet bust of 2000, and the Panic of 2008). Apart from those extreme events, the P/E ratios of 19x to 25x are relatively high. Is this a run-up to another bubble? What questions should the canny observer ask about high P/E ratios?
Let me frame a (wonkish) reply in terms of finance theory, which suggests that the size of a multiple is driven by two main factors: risk and expected growth. For instance, the widely-used Price/Earnings multiple can be decomposed into two factors:
Stock Price/E(EPS) = 1/r + PVGO/E(EPS)
E(EPS) is the earnings per share expected to be reported next year. The factor “r” is the required return on equity, which is determined by risk. And PVGO  is the present value of growth opportunities per share, an estimate of today’s value of investments expected to be made in the future. The term, “growth company,” is not defined by the growth rate of sales, earnings or assets, but by the size of PVGO relative to the market value of equity.
In other words, the P/E ratios of “growth firms” are typically sizable, and driven significantly by attractive future growth opportunities. One can decompose other ratios in a similar fashion. But the key idea is that multiples reflect important economic phenomena. To judge whether a multiple is appropriate, one should look into the underlying economic fundamentals and critically evaluate the assumptions of the model. 
So, let’s consider the possibilities. Suppose that “r” is 10%, the going risk-adjusted rate of equity return for the average low-growth firm, such as a public utility. Therefore, 1/r would equal 10.0. Compared to the average P/E ratios for the S&P500 (either 19 or 25), this implies that the present value of growth opportunities these days is simply enormous, accounting for 45-60% of the value of the S&P500. What might explain this huge growth component?
One possibility that you hear mooted on financial talk shows is that the market is “overheated,” “getting ahead of its skis,” and even, “a bubble.” We’ve certainly seen frothy conditions before and shouldn’t be surprised to see them again. The problem is that you could summon up some kind of psychological explanation for market conditions virtually any time. Psychology is always useful as a warning flag; but it won’t tell the investor exactly what to do. Generally, if you think that the market is getting overheated, you might cash out, buy put options, or sell short. But research suggests that trying to time the market by trading actively is an easy way to lose money.
A second possibility is that investors embrace some realistic growth phenomena that justify these huge PVGOs. If so, the canny investor should try to identify the source of these growth opportunities. One helpful resource will be this year’s University of Virginia Investing Conference —November 13-14—the theme of which will be “Investing in Innovation.” Innovation is perhaps the most important foundation for growth, and PVGO. The conference will offer insights about growth prospects in fields such as information technology, energy, health care, and monetary policy. Once again, we are booking an impressive collection of speakers. As of today, speakers will include these (additional speaker are in the offing):
- Charles R. Cory (MBA ’82), Chairman of Global Technology Investment Banking & Managing Director, Morgan Stanley
- Richard Fisher, President & CEO, Federal Reserve Bank of Dallas (schedule pending)
- W. Barnes Hauptfuhrer (MBA/JD ’81), Chief Executive Officer, Chapter IV Investors
- Robert J. Hariri, Founder, Chairman & Chief Scientific Officer, Celgene Cellular Therapeutics
- Ned Hooper (MBA ’94), Partner, Centerview Capital
- Robert J. Hugin (MBA ’85), Chairman & CEO, Celgene Corporation
- Samuel D. Isaly, Managing Partner, OrbiMed
- Nancy Lazar, Partner, Cornerstone Macro
- John Siegel, Partner, Columbia Capital
- Michael Sola, Portfolio Manager, T. Rowe Price
- Kathy Warden, Corporate Vice President and President, Northrop Grumman Information Systems
“Early bird” registration discounts end tomorrow, August 8th. Sign up this week to get the highest return on your conference investment.
In all probability, today’s high P/E multiples are due to a blend of buoyant investor psychology and genuine growth opportunities. If so, this puts a high premium on thinking critically about investment themes, trends, and market sentiment. Conferences are one excellent means of sharpening your own thinking. Join us in November!
- Stewart Myers originally suggested the important role of growth options in the valuation of the firm. See his paper, “Determinants of Corporate Borrowing,” Journal of Financial Economics, 5:146-175 (1977). The decomposition of P/E presented here is discussed more fully by Myers in his book with Richard Brealey and Franklin Allen, Principles of Corporate Finance. [↩]
- Though widely used, and simple to use, investing on the basis of P/E multiples is vulnerable to several potential problems, such as the dependence on GAAP accounting practices, which afford managers rather wide latitude in reporting the financial results of the firm. Also, the P/E ratio can be computed using backward-looking or forward-looking earnings. For growing firms, the difference in financial performance between the year just past and the year ahead will be material. In addition, a focus on Earnings per Share ignores important effects of capital investment, investment in working capital, and depreciation. [↩]