Predictions versus Forecasts

A favorite pastime of market pundits is making sport of those who do forecasting, especially if models are involved.  I am continually amazed at the delight people take in criticizing things where they have no information.  The ongoing mission at "A Dash" is to discover and exploit such errors.

Background Example

Let us suppose that we have a city in an earthquake zone.  There is a fault line.  Our job is to predict something mundane, like revenue over a toll bridge.  We may use various factors to predict traffic and revenue as the basis for the forecast.  Meanwhile, we all know that there is earthquake potential.  If and when the earthquake comes, the revenue forecast will be seriously wrong.

So we could make a prediction:  There will be an earthquake in the next ten years.

Or we can make a forecast:  Here is the expected bridge traffic next year.

Please note that the forecaster is usually correct by ignoring the earthquake.  If he decides to include it, he can be wrong in one of two ways:

  • He can deduct something from each year's forecast, making them all incorrect by 10% or so; or
  • He can guess the year of the quake. He will be correct one year in ten and wrong in the other years.

Let me consider how people mistakenly confuse the two approaches in analyzing the stock market.

A Conversation with George

(This is a composite conversation with real people, but not a specific one.  It is accurate, in that it reflects the feelings of many, but it is not an actual dialog.)

I got a call from George, an intelligent market observer who reads a lot.

G:  What do you think about the market?  I am getting worried after the big move.

J:  Are you all-in?

G:  Are you kidding?  I am not in at all.  I just heard a prediction that the S&P 500 is going to 400.

J:  Who said that?

G:  Someone with a system.  He said to ignore predicted earnings because analysts are biased.  He uses only actual known earnings.  Everything else is a lie.  His history went back to the time of Paul Revere or something — great research.  He also pointed out that we had to use a "trough multiple" — or — just a second — that was what we used last year.  Now we should use the peak multiple, but they are actually both the same.  You multiply $50 in S&P earnings by 8, and that is what the market should be.  Do you know what the P/E ratio was in 1840?

J:  Uh…  May we return to the 21st century?

G:  I thought you were a scholar.  But OK.

J:  It has taken 18 months to regain the pre-Lehman levels.  The selling in late '08 and early '09 were predictions of another depression and a total failure of the Obama Administration.  It has taken this long to return to a semblance of sanity.

G:  So what?  There is always a correction after a big move.  We are going lower.  Much, much lower.

J:  Markets do not go straight up, but we are just getting back to a starting point, something that I described as an "initial target" at the start of 2009.  Nearly every indicator, except employment, is better than it was then.  Markets are about earnings, and earnings are showing great strength.

G:  I think that the market will move sideways for many years — or maybe sell off.

J:  Why?

G:  The economy cannot  grow without the consumer.  I read that consumers are 70% of the economy and that they are tapped out, spent up, unemployed, and leveraged to the hilt.  the market is going nowhere without the consumer.

J:  The mainstream economic forecasts…..

G:  Forecasts!  Don't give me that!  Those economists know nothing!  They know nothing!  They did not see it coming. They use models.  That is just fantasyland.  Everyone knows that models have built-in error.  Economists know nothing.  Obama knows nothing.  Congress knows less than nothing.  These are the guys who got us into trouble and I am not going to believe them.

J:  OK.  Let us put aside the political and methodological rant.

G:  It is just the truth.  We will be lucky to stay sideways in this market.  I have actually been checking out the price of farmland.

J:  How is your ammo?

G:  Locked and loaded.

J:  Returning to the market, you just told me what you expect.  How did you arrive at those conclusions?

G:  I read some great sources, including many who predicted the crash.  They explain that the forecasters are all wrong.  None of the models worked.  The guys I read all saw it coming.

J:  Did any of them change their opinions at any point?  After the fall of Lehman?  After the government policy actions?  After improving economic data?

G:  Change?  No way!!  They got it right.  Lehman and that other stuff made no difference.


The Dilemma

As an investment advisor, how do you help someone with this mind set?   There are several very fundamental problems.  Let me take them one at a time.

Predictions are often very general and completely ignore the time frame.  We started seeing recession forecasts in 2004 or so.  Keeping in mind that a recession happens (on average) every five years, what should be the shelf life for these predictions?  Those who grew impatient started arguing their own definitions for what constituted a recession.

Predictions involve modeling.  The difference is that for many people the models are poorly specified, based on little information, and cannot be tested.  Consider George's assertions.  He actually made a commonly-accepted statement that has hidden modeling and assumptions.

  • Economy and the consumer.  Those who cite the 70% statistic do some while ignoring a long list of assumptions.  Most consumer spending holds up even in recession.  Not everyone is affected, and even those who are have various means of support.  There are also new population entrants.  Finally, there are times when business takes the lead, and we might be in such a cycle.
  • Economy and the stock market.  Those who point to economic concerns think that the market is a GDP future.  This is quite clearly not correct.  Many companies can and do thrive even in adverse economic circumstances.

My point is not that the predictions from George's pundits will be wrong.  The point is that the reasoning is very sloppy.

Anyone making a prediction is using a model!

Those who make predictions while criticizing modelers simply lack the requisite training.  A professional modeler identifies risks and possible error.  Every modeler understands that the result is a simplification of reality.  Good modelers test results against reality and suggest error ranges.

Compare this highly professional approach with the "laundry list" method of many pundits who have no formal training in models.  They cite lists of "headwinds" and make predictions without time frames.  Those who rail against models and the "folly of forecasting" while still making predictions are still doing modeling, but doing it very poorly.

There will be an earthquake some day…..

Investment Conclusion

Investors should be paying attention to the analysis of the causes of the financial crisis.  There is a complex story including many factors.  Understanding what happened could be important to making the right investment choices.

So how should I explain this to George, whose mind is made up?

You may also like


  • Trading Goddess April 22, 2010  

    Thanks! Keep up the good work!

  • Mike C April 22, 2010  

    So how should I explain this to George, whose mind is made up?
    Is this a rhetorical question? If George isn’t a client, then it probably isn’t that important.
    Just read the Big Short the other day. The book opens with a quote from Tolstoy that I think is one of the best I’ve ever read and is directly applicable to your question about George, and perhaps also to someone with the absolute polar opposite view from George.
    There is only one thing I am certain of in this current economic/stock market backdrop, and that is that it has the potential to make fools out of both doom and gloomers calling for S&P 400 and also those who think “America is back to “NORMAL”” where normal means the economy and market of the last 20 years.
    My own view and what I would tell George is that now is the time to be humble in what you think you know and what you do not know, especially the “unknown unknowns” to steal from Rumsfeld.
    One can cite a litany of studies, evidence, metrics on both sides, and it isn’t just pundits citing headwinds (Reinhart and Rogoff).
    Meanwhile, I would point out to George that many statistics support a bullish outlook. As Ned Davis would say, I would ask George, do you want to be right or make money?
    I remain cautiously optimistic and bullish, mostly invested with clear-cut risk management rules in place just in case George’s “guy with a system” turns out to be right.
    My final question to George would be do you want to make your investment decisions on opinions or data? Follow the preponderance of the data and the trend.

  • Mike C April 22, 2010  

    BTW, in the spirit of giving credit where credit is due, great call/stance on Apple which you’ve mentioned a number of times.
    What are some other individual names you like here?

  • Jeff Miller April 22, 2010  

    Mike C — I am still with my 2010 forecast picks. I love the Windows 7 upgrade cycle and everything linked to it. You are getting a chance to buy these names — like last year — and also some attractive health care stocks in hospitals, devices, managed care and related fields.
    Thanks for the recognition on Apple. Holding on to winners as the story improves is one of the big challenges.

  • walt April 23, 2010  

    Jeff: did your forecasts include widespread fraud in writing mortgages? It sounds to me like your models are little more than cycles of data, by definition from the past. Are you including the price of energy?
    I see Hussman as the anti-Jeff. He is a perma-bear who is never wrong, but never right, and just keeps collecting his fees.

  • yourpaldal April 23, 2010  

    Hopefully Jeff has been wise enough not to take George as a client. George isn’t going to get it. Discuss the weather with him and wish him a good day.