Mod Note (Andy): This was originally posted on his blog on June 16th
If you believe that the stock market is in a bubble, you have lots of company. You have long-time market watchers, the New York Times and even a Nobel Prize winner in your camp. But what exactly is a bubble? How can you tell if you are in one? And if you do believe you are in a bubble, what is your best course of action? Not only are these questions difficult to answer, but the answers can vary across markets, investors and time.
The Bubble Machine
- Doomsday Bubblers have been warning us that the stock market is in a bubble for as long as you have known them, and either want you to keep your entire portfolio in cash or in gold (or bitcoins). They remind me of this character from Winnie the Pooh and their theme seems to be that stocks are always over valued.
- Knee Jerk Bubblers go into hibernation in bear markets but become active as stocks start to rise and become increasingly agitated, the more they go up. They are the Bobblehead dolls of the bubble universe, convinced that if stocks have gone up a lot or for a long period, they are poised for a correction.
- Armchair Psychiatrist Bubblers use subtle or not-so-subtle psychological clues from their surroundings to make judgments about bubbles forming and bursting. Freudian in their thinking, they are convinced that any mention of stocks by shoeshine boys, cab drivers or mothers-in-law is a sure sign of a bubble.
- Conspiratorial Bubblers believe that bubbles are created by small group of evil people who plan to profit from them, with the Illuminati, hedge funds, Goldman Sachs and the Federal Reserve as prime suspects. Paranoid and ever-watchful, they are convinced that stocks are manipulated by larger and more powerful forces and that we are all helpless in the face of this darkness.
- Righteous Bubblers draw on a puritanical streak to argue that if investors are having too much fun (because stocks are going up), they have to be punished with a market crash. As the Flagellants in the bubble world, they whip themselves into a frenzy, especially during market booms.
- Rational Bubblers uses market metrics that are both intuitive and widely used, note their divergence from historical norms and argue for a correction back to the average. Viewing themselves as smarter than the rest of us and also as the voices of reason, they view their metrics as infallible and mean reversion in markets as immutable.
Defining a Bubble
Detecting a Bubble
The benefits of being able to detect a bubble, when you are in in its midst rather than after it bursts, is that you may be able to protect yourself from its consequences. But are there any mechanisms that detect bubbles? And if they exist, how well do they work?
a. PE and variants
In the graph below, I report on the time trends between 1969 and 2013 in four variants of the PE ratios, a PE using trailing 12 month earnings (PE), a PE based upon the average earnings over the previous ten years (Normalized PE), a PE based upon my estimates of inflation-adjusted average earnings over the prior ten years (My CAPE) and the Shiller PE.
|Normalized PE used average earnings over last 10 years & My CAPE uses my inflation adjusted normalized earnings. Shiller PE is as reported in his datasets|
|T statistics in italics below each correlation; numbers greater than 2.42 indicate significance at 2% level|
First, the negative correlation values indicate that higher PE ratios today are predictive of lower stock returns in the future. Second, that correlation is weak with one-year forward returns (notice that none of the t statistics are significant), become stronger with two-year returns and strongest with three-year returns. Third, there is little in this table to indicate that normalizing or inflation adjusting the PE ratio does much in terms of improving its use in prediction, since the conventional PE ratio has the highest correlation with returns over time periods
|PE measures: 1969-2013|
|One-year and Two-year stock returns|
b. EP Ratios and Interest Rates
This insight is not new and is the basis for the Fed Model, which looks at the spread between the EP ratio and the T.Bond rate. The premise of the model is that stocks are cheap when the EP ratio exceeds T.Bond rates and expensive when it is lower. To evaluate the predictive power of this spread, I classified the years between 1969 and 2013 into four quartiles, based upon the level of the spread, and computed the returns in the years after (one and two-year horizons):
The results are murkier, but for the most part, stock returns are higher when the EP ratio exceeds the T.Bond rate.
c. Intrinsic Value
Both PE ratios and EP ratio spreads (like the Fed Model) can be faulted for looking at only part of the value picture. A fuller analysis would require us to look at all of the drivers of value, and that can be done in an intrinsic value model. In the picture below, I attempt to do so on June 14, 2014:
|Intrinsic valuation of S&P 500: June 2014|
The current implied ERP of 4.99% is well above the historic average and median and it clearly is much higher than the 2.05% that prevailed at the end of 1999.
Are we in a bubble?
In the table below, I summarize where the market stands today on each of the metrics that I discussed in the last section:
Bubble Belief to Bubble Action: The Trade Off
- The cost of acting: If you decide to act on a bubble, there is a cost. With the passive defense, the money that you take out of equities has to be invested somewhere safe (earning a risk free rate, or something close to it) and if the correction does not happen, you will lose the return premium you would have earned by investing stocks. With an active defense, the cost of being wrong about the correction is even greater since your losses will increase in direct proportion with how well stocks continue to do. (Note that using derivatives to protect yourself against market corrections or for speculation will deliver variants of these defenses.)
- The benefit of acting: If you are right about the bubble and a correction occurs, there is a payoff to acting. With the passive defense, you protect your investment (or at least that portion that you shift out of equities) from the drop. With the active defense, you profit from the drop, with the magnitude of your profits increasing with the size of the correction.
To illustrate the trade off, consider a simple (perhaps simplistic) scenario, where you are fully invested in equities and believe that there is 20% probability of a market correction (which you expect to be 40%) occurring in 2 years. In addition, let's assume that the expected return on stocks in a normal year (no bubble) is 7.51% annually and that the expected annual return if a bubble exists will be 9% annually, until the bubble bursts. In the table below, I have listed the payoffs to doing nothing (staying 100% in equities) as well as a passive defense (where you sell all your equity and go invest in a risk free asset earning .5%) and an active defense (where you sell short on equities and invest the proceeds in a risk free asset):
|Future value of portfolio in 2 years (when correction occurs)|
If you remain invested in equities (do nothing), even allowing for the market correction of 40% at the end of year 2, your expected value is $1.0672 at the end of the period. With a passive defense, you earn the risk free rate of 0.5% a year, for two years, and the end value for your portfolio is just slightly in excess of $1.01. With an active defense, where you sell short and invest int he risk free rate, your portfolio will increase to $1.3072, if a correction occurs, but the expected value of your portfolio is only $0.9528, which is $0.1144 less than your do-nothing strategy.
If you feel absolute conviction about the existence of a bubble and see a large correction coming immediately or very soon, it clearly pays to act on bubbles and to do so with an active defense. However, that trade off tilts towards inaction as uncertainty about the existence of the bubble increases, its expected magnitude decreases and the longer you will have to wait for the correction to occur. I know that I am pushing my luck here but I tried to assess the trade off in a spreadsheet, where based upon your inputs on these variables, I estimate the net benefit of acting on a bubble for the passive act of moving all of your equity investment into a risk free alternative:
|Payoff to Passive Defense against Bubble (Correction of 40% in 2 years)|
The net payoff to acting on a bubble generates positive returns only if your conviction that a bubble exists is high (with a 20% probability, it almost never pays to act) and even with strong convictions, only if the market correction is expected to be large and occur quickly.
Bubblenomics: My perspective
It is extremely dangerous to disagree with a Nobel prize winner, and even more so, to disagree with two in the same post, but I am going to risk it in this closing section:
- There will always be bubbles: Disagreeing with Gene Fama, I believe that bubbles are part and parcel of financial markets, because investors are human. More data and computerized will not make bubbles a thing of the past because data is just as often an instrument for our behavioral foibles as it is an antidote to them and computer algorithms are created by human programmers.
- But bubbles are not as common as we think they are: Parting ways with Robert Shiller, I would propose that bubbles occur infrequently and that they are not always irrational. Most market corrections are rational adjustments to real world shifts and not bubbles bursting and even the most egregious bubbles have rational cores.
- Bubbles are more clearly visible in the rear view mirror: While bubbles always look obvious in hindsight, it is far less obvious when you are in the midst of a bubble.
- Bubbles are not all bad: Bubbles do create damage but they do create change, often for the better. I do know that the much maligned dot-com bubble changed the way we live and do business. In fact, I agree with David Landes, an economic historian, when he asserts that "in this world, the optimists have it, not because they are always right, but because they are positive. Even when wrong, they are positive, and that is the way of achievement, correction, improvement, and success. Educated, eyes-open optimism pays; pessimism can only offer the empty consolation of being right." In market terms, I would ratherhave a market that is dominated by irrationally exuberant investors than one where prices are set by actuaries. Thus, while I would not invest in Tesla, Twitter or Uber at their existing prices, I am grateful that companies like these exist.
- Doing nothing is often the best response to a bubble: The most rational response to a bubble is to often not change the way you invest. If you believe, as I do, that it is difficult to diagnose when you are in a bubble and if you are in one, to figure when and how it will dissipate, the most sensible response to the fear of a bubble is to not change your or investment philosophy. Conversely, if you feel certain about both the existence of a bubble and how it will burst, you may want to see if your certitude is warranted given your metric.