Confusing and frustrating as it may be, the answer about the current valuation of stocks will always be different depending on who you ask. Various economists, mutual fund portfolio managers, research analysts, financial news print and TV personalities, and other parties seem to disagree on this very important question.  Financial professionals will offer a wide range of financial and economic statistics in support of these opinions on the current valuation of stocks.  One of the most often cited statistics in support of a person’s opinion is the P/E ratio of the stock market at any given point in time.   Many financial professionals use it as one of the easiest numbers to be able to formulate a viewpoint on stock valuation.  However, when it comes to any statistic, one must always be skeptical in terms of both the way the number is calculated and its predictive value.  Any time one number is used to describe the financial markets one must always be leery.  A closer examination of the P/E ratio is necessary to show why its usage alone is a poor way to make a judgement in regard to the proper valuation of stocks.

The P/E ratio is short for Price/Earnings ratio. The value is calculated by taking the current stock price divided by the annual earnings of the company.  When it is applied to an entire stock market index like the S&P 500 index, the value is calculated by taking the current value of the index divided by the sum of the annual earnings of the 500 companies included in the index.  One of the very important things to be aware of is that the denominator of the equation may actually be different depending on who is using the P/E ratio.  Some people will refer to the P/E ratio in terms of the last reported annual earnings for the company (index).  Other people will refer to the P/E ratio in terms of the expected earnings for the company (index) over the next year.  In this particular case, the P/E ratio is referred to as the Forward P/E ratio.  Both ratios have a purpose.  The traditional P/E ratio measures the reported accounting earnings of the firm (index).  It is a known value.  The Forward P/E ratio measures the profits that the firm (index) will create in the future.  However, the future profits are only a forecast.  Many analysts prefer to use the Forward P/E ratio because the value of any firm (or index of companies) is determined by its future ability to generate profits for its owners.  The historical earnings are of lesser significance.

The P/E ratio is essentially a measure of how much investors value $1 worth of earnings and what they are willing to pay for it. For example, a firm might have a P/E ratio of 10, 20, 45, or even 100.  In the case of a firm that is losing money, the P/E ratio does not apply.  In general, investors are willing to pay more per each $1 in earnings if the company has the potential to grow a great deal in the future.  Examples of this would be companies like Amazon (Ticker Symbol:  AMZN) or Netflix (Ticker Symbol:  NFLX) that have P/E ratios well over 100.  Some companies are further along in their life cycle and offer less growth opportunities and tend to have lower P/E ratios.  Examples of this would be General Motors or IBM that have P/E ratios in the single digits or low teens, respectively.  Investors tend to pay more for companies that offer the promise of future growth than for companies that are in mature or declining industries.

When it comes to the entire stock market, the P/E ratio applied to a stock market index (such as the S&P 500 index) measures how much investors are willing to pay for the earnings of all the companies in that particular index. For purposes of discussion and illustration, I will refer to the S&P 500 index while discussing the P/E ratio.  The average P/E ratio for the S&P 500 index over the last 40 years (1966-2015) was 18.77.  When delivering an opinion on the valuation of the S&P 500 index, many financial professionals will cite this number and state that stocks are overvalued (undervalued) if the current P/E ratio of the S&P 500 index is above (below) that historical average.  If the current P/E ratio of the S&P 500 index is roughly in line with that historical average, the term fairly valued will usually be used in relation to stocks.  The rationale is that stocks are only worth what their earnings/profits are over time.  There is evidence that the stock market can become far too highly priced (as in March 2000 or December 2007) or far too lowly priced (as in 1982) based upon the P/E ratio observed at that time.  Unfortunately, the relative correlation between looking at the difference between the current P/E ratio of the stock market and the historical P/E ratio does not work perfectly.  In fact, it is only under very extreme circumstances and with perfect hindsight that investors can see that stocks were overvalued or undervalued in relation to the P/E ratio at that time.

Here are the historical P/E ratios for the S&P 500 index from 1966-2015 as measured by the P/E ratio at the end of the year. Additionally, the annual return of the S&P index for that year is also shown.

Average             18.77

The P/E ratio for the S&P 500 index has varied widely from the single digits to values of 40 or above. The important thing to observe is that very high P/E ratios are not always followed by low or negative returns, nor are very low P/E ratios followed by very high returns.  In terms of a baseline, the S&P 500 index returned approximately 9.5% over this 40-year period.  As is immediately evident, the returns of stocks are quite varied which is what one would expect given the fact that stocks are known as assets that exhibit volatility (meaning that they fluctuate a lot because the future is never known with certainty).  Thus, whenever a financial professional says that stocks are overvalued, undervalued, or fairly valued at any given point in time, that statement has very little significance.  Whenever only one data point is utilized to give a forecast about the future direction of stocks, an individual investor needs to be extremely skeptical of that statement.  The P/E ratio does hold a very important key for the future returns of stocks but only over long periods of time and certainly not over a short timeframe like a month, quarter, or even a year.

An improvement on the P/E ratio was developed by Dr. Robert J. Shiller, the Nobel Prize winner in Economics and current professor of Economics at Yale University. The P/E ratio that Dr. Shiller developed is referred to as the Shiller P/E ratio or the CAPE (Cyclically Adjusted Price Earnings) P/E ratio.  This P/E ratio takes the current value of a stock or stock index and divides it by the average earnings of a firm or index components for a period of 10 years and also takes into account the level of inflation over that period.  The general idea is that the long-term earnings of a firm or index determine its relative valuation.  Thus, it does a far better job of measuring whether or not the stock market is fairly valued or not at any given point in time.  However, another very important piece of the puzzle has to do with interest rates.  Investors are generally willing to pay more for stocks when interest rates are low than when interest rates are high.  Why?  If it is assumed that the future earnings stream of the company remains the same, an investor would be willing to take more risk and invest in stocks over the safety of bonds.  A quick example from everyday life is instructive.  Imagine that your friend wants to borrow $500 for one year.  How much interest will you charge your friend on the loan?  Let’s say you want to earn 5% more than what you could earn by simply buying US Treasury Bills for one year.  A one-year US Treasury Bill is risk free and, as of May 10, 2016 yields interest of 0.50%.  Therefore, you might charge your friend 5.5% on the loan.  Now back in the early 1980’s, one-year US Treasury Bills (and even savings accounts at banks) were 10% or higher.  If you were to have provided the loan to your friend then, you would not charge 5.5% because you could simply deposit the $500 in the bank.  You might charge your friend 15.5% on the loan assuming that the relative risk of your friend not paying you back is the same in both time periods.  It is very similar when it comes to investing in stocks.  Due to the fact that stocks are volatile and future profits are unknown, investors tend to prefer bonds over stocks as interest rates rise.  This phenomenon causes the value of stocks to fall.  Conversely, as interest rates fall, the preference for bonds decreases and investors will choose stocks more and prices go up.  Now this assumes that the future earnings of the company or index constituents stay the same in either scenario.

With that information in mind, a better way to gauge the relative valuation of stocks in terms of being overvalued, undervalued, or fairly valued, would be to look at the Shiller P/E ratio in combination with interest rates. It is most common for investors to utilize the 10-year US Treasury note as a proxy for interest rates.  Here are the historical values for the Shiller P/E ratio and the 10-year US Treasury note over the same 40-year period (1966-2015) as before:

Average                19.80                          6.44%

These two data points provide a much better gauge of whether or not stocks are currently overvalued or undervalued. For example, take a look at the Shiller P/E ratio in the late 1970’s and early 1980’s.  The value of the Shiller ratio is in the single digits during this time period because interest rates were higher than 10%.  Lately interest rates have been right around 2.0%-2.5% for the past several years.  Therefore, one would expect that the Shiller P/E ratio would be higher.  Now the historical average for the Shiller P/E ratio was 19.80 over this period.  The Shiller P/E ratio was in the neighborhood of 40 during 1998-2000 which preceded the bursting of the Internet Bubble in March 2000.  The Shiller P/E ratio was at its two lowest levels of 7 and 8 in 1981 and 1982, respectively which is when the great bull market began.  However, while this Shiller P/E and interest rates are better than simply the traditional P/E ratio, there are flaws.  The Shiller P/E in 2007 was 24.02 right (and interest rates were around 4.0% which is on the low side historically) before the huge market drop of the Great Recession between September 2008 and March 2009.  In fact, the S&P 500 index was down over 37% in 2008, and the Shiller P/E did not provide an imminent warning of any such severe downturn.  Therefore, even looking at these two measures is imperfect but better than the normal P/E ratio in isolation.

To summarize the discussion, individual investors will always be told on a daily basis by various sources that the stock market is currently overvalued, undervalued, and fairly valued at the same time. One of the most commonly used rationales is a reference to the current P/E ratio in relation to the historical P/E ratio.  As we have seen, this one data point is a very poor indicator of the future direction and relative value of stocks at any given period of time, especially for short periods of time (one year or less).  The commentary and opinions provided by financial “experts” to individual investors when the P/E ratio is mentioned normally relates to the short term.  By looking back at the historical data, it is clear that this one data point is really only relevant over very long periods of time.  The Shiller P/E ratio in combination with current interest rates is a great improvement over the traditional P/E ratio, but it is even imperfect when it comes to forecasting the future returns of the stock market.  There are two general rules for individual investors to take away from this discussion.  Whenever a comment is made about the current value of stocks and only one statistic is provided, the opinion should be taken with a “grain of salt” and weighed only as one piece of information in determining investment decisions that individual investors may or may not make.  Additionally, and equally as important, if a financial professional cites a statistic about stock valuation that you do not understand (even after doing some research of your own), you should always discard that opinion in most every case.  Individual investors should not make major investment decisions in terms of altering large portions of their investment portfolios of stocks, bonds, and other financial assets utilizing information that they do not understand.  It sounds like common sense, but, in the sometimes irrational world of investing, this occurrence is far more common than you imagine.