The merit of the Shiller p/e, which is backward looking, for timing investment decisions is cautioned against even by its supporters like John Hussman. It's something of a straw man to attack people like him for using it that way when they really don't use it to time market entry and exit points. Hussman views the indicator as one of a number of things which help him forecast 10-year returns going forward, a point lost it seems on people who don't read him carefully. High Shiller p/e levels in the present are part of an ensemble of indicators which to Hussman forecast low average annual returns over the course of the next decade.
That said, which has been the better indicator for timing a major allocation of monies to stocks in the recent past, the backward-looking Shiller p/e or the simple S&P500 p/e?
Today's Shiller p/e is a very high 26.06, 57.65% above its mean level of 16.53. The S&P500 p/e is 19.32, 24.56% above its mean level of 15.51. By both measures, today would seem to be a costly time to invest new monies in the stock markets.
How about during the March 2009 period when stocks tanked to their lows during the financial crisis?
The Shiller p/e actually told you to invest, hitting 13.32 on March 1, just days before the markets bottomed. In fact between October 2008 and June 2009 the indicator remained at or below 16.38, in other words below mean level, while the S&P500 inverted bell curve fell from 1100 to 683 and rose to 940. With the S&P500 now over 1900, any time during that woeful period looks in retrospect like a great time to buy. The trouble was that people didn't have any money to invest, being fully invested as usual, riding it all the way down after riding it all the way up.
The S&P500 p/e on the other hand was quite high on March 1, 2009 at 110.37, 612% above its mean level! It most definitely told you NOT to buy then, when you should have bought then. This indicator didn't hit its lows for the period, at the 13 level, until the late summer of 2011 and then only briefly, when interestingly enough the S&P500 was trading near 1100 again, in retrospect another very good time to buy. But at that time the Shiller p/e was above mean, at about 20, and you might have been forgiven for not taking the bait. But because you didn't you've missed an 800 point climb in the S&P500.
You have to go all the way back to the late 1980s to get an S&P500 p/e ratio consistently below 15, and even earlier to the mid-1980s for the Shiller p/e. All of which is to say that stocks have been rather expensive for quite a long time in general, coinciding with the generational focus on it as the way to make the big money for retirement.
In other words, we're in a bubble, and we blew it.
