By Michael J. Wiener
Special to the Financial Independence Hub
Wouldn’t it be great if we could predict the future movements of stock markets so we could capture the gains and avoid the losses? It turns out we can’t, but that doesn’t stop people from trying.
After a Twitter exchange with John De Goey, I ended up reading the article The Remarkable Accuracy of CAPE as a Predictor of Returns by Michael Finke. He gives a chart that appears to show we can predict the coming decade of stock returns by calculating what is known as the CAPE (Cyclically Adjusted Price-to-Earnings Ratio).
For our purposes, we don’t need to know much about the CAPE other than that it is a measure of how expensive stocks are and that it was invented by Robert Shiller, who received a Nobel Prize in Economics in 2013. In fact, we don’t even have to calculate the CAPE ourselves; it is freely available and updated daily.
Right now, stock prices are very high. As I write this, the CAPE for U.S. stocks stands at 37. The only time it was higher in the past century was during the tech boom and bust around the year 2000. We seem to be repeating the boom part, and the fear is that we may soon repeat the bust part.
Here is my reproduction of a chart similar to Finke’s chart:
Finke’s chart used nominal U.S. stock returns rather than real (inflation-adjusted) returns, but they show the same thing: an apparently close relationship between the CAPE and U.S. stock returns over the subsequent decade. Given the current CAPE, stock returns appear to be predictable to within +/- 3% per year. That would be amazingly accurate if true.
Based on this chart and the fact that the CAPE is currently 37, we’d expect the average annual stock return in the next 10 years to be between inflation minus 4% and inflation plus 1.5%. If true, this would clearly mean it makes sense to sell stocks. De Goey made his position clear in an article titled Get Out!.
Sadly, there holes in this story. Nobel Prize winner Shiller invented the CAPE, but he isn’t involved with Finke’s paper, despite De Goey’s implication when he defended Finke’s chart saying “Oh, and the guy who came up with the concept has a Nobel Prize.”
You might wonder how the chart above has so many points when we’re talking about 10-year returns and it covers only 25 years of stock market data. The answer is that the chart uses 300 overlapping 10-year periods. So, each point represents a starting month. Two successive months are likely to have nearly the same CAPE and nearly the same 10-year annual returns. So, we get lots of bunched up dots.
But the truth is that we have very little data. We really only have two independent 10-year periods. Despite the impressive correlation the chart shows, we’re extrapolating from little information.
To show the problem, let’s repeat this chart for another time period:
I didn’t choose this date range at random; I selected it to make a point. If we were to devise a strategy based on this chart, we’d say not to worry if the CAPE gets high because you’ll still get decent returns. But when the CAPE is in the 17 to 18 range, stocks are either going on a big run, or they’ll crash, and you have to be ready to get out. This is obviously nonsense. It’s dangerous to try to build strategies on too little information.
Here’s a chart using S&P 500 stock data from 1936 to the present:
This data still only covers seven independent decades, but we can see the real picture of the relationship between the CAPE and stock returns is a lot fuzzier than the first chart made it seem. We can still reasonably guess that a higher CAPE reduces future expected stock returns, but the range of returns is still wide. Continue Reading…














