Returns and the Law of Averages

February 26, 2017

Value.  How do we gauge it?  What if we know that we are probably not getting the best value at the time?  What should we do?  A common metric used to value stocks – the Shiller CAPE ratio – indicates that we can expect lower returns in the future.  Should we change our behavior?

We calculate a Price/Earnings (P/E) ratio by dividing the current price of a stock by the last 12 months of the stock’s earnings. The Shiller Cyclically Adjusted P/E ratio (CAPE) searches for the signal amid the noisy static of quarterly earnings, the divisor in the P/E formula. Seasonal variations and the normal fluctuations in the business cycle give some erraticness to quarterly earnings. To uncover the signal, we divide the inflation-adjusted average of the past ten years of earnings. With that more stable figure as the divisor, we can more easily understand the variations in price relative to that stable base.

As I wrote last week, the CAPE is at the third highest peak of the past century, just below the peak at the 1929 market crash.

Conclusion: stocks are seriously overvalued.

Argument: The past ten years of earnings include the financial crisis, the 2nd most severe downturn of the past century. That skews the CAPE ratio higher, so stocks aren’t overvalued.

CounterArgument: OK fine. Let’s use a 5 year CAPE ratio which excludes the financial crisis and the following two years. In the chart below, both ratios are shown. We are missing firm figures for last quarter’s earnings from S&P, but 82% of companies have reported earnings for the 4th quarter. Based on that known data, FactSet projects 4.6% earnings growth for the index as a whole. I have used that as a reasonably close estimate.

The 40 year average of the conventional 10 year CAPE, or CAPE10, is 20.8. The current CAPE10 is about 29 based on earnings estimates. The 40 year average of the 5 year CAPE, or CAPE5, is 19.6. The current CAPE5 is 24.8. Even the 5 year average indicates that the market is priced to perfection, about 26% more than the 40 year history.

Revised Conclusion: Based on the past 40 years of historical data, the market is over-priced, using both a short and long term approach.

There’s one more metric: ROI, or Return on Investment, a simple guideline that we can compute by excluding dividends and dividing today’s stock price by a previous price. For example, if I bought a stock at $100 on January 1, 2000 and sold it at $120 on January 1, 2005, I have made 20% / 5 years = 4% per year.

Over the past 40 years, the average of this simple 5 year ROI is 10.46%. The current 5 year ROI is 14%, 3.5% above the average. The 7% correction of last winter, from early January to early March, brought us to within range of the 40 year average.

Revised and Confirmed Conclusion: Mr. Market is over-priced.

There is a data tidbit that makes future returns a little bit more predictable, and it involves the law of averages. As I noted, the current 5 year ROI is computed by dividing today’s price by the price 5 years ago. Future ROI is a stock price 5 years in the future divided by the current price. In the 35 years from 1977 through early 2012, the average of the future ROI + current ROI is 10.9%, just slightly above the 40 year average of current ROI.

What this means is that if the current 5 year ROI is 14%, or 3.5% above average, there is a tendency toward a lower than average  return for the next 5 years. However, returns can be far above average and below average for an extended period of time. The dot-com boom from 1995 to 2001 had a series of extremely high 5 year ROI values, and might have convinced some investors that they were stock-picking geniuses.


Returns were astronomically high.  Unfortunately, the following 6 years from late 2001 to 2007 had low returns.

After several months of above average 5 year ROI returns, another 6 year depression on the heels of the financial crisis.

Conclusion with Reflection: For the long term investor (more than 5 years), a broad based index of stocks like the SP500 provides consistent returns that beat most passive investments. The cyclic ups and downs should not distract us from this central fact.  The law of averages can help us develop reasonable expectations of future returns.  By understanding the balance of above and below average, we do not become overly optimistic or pessimistic.



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