Investor Irrationality
Historians who have examined the behavior of
financial markets over time have challenged the assumption of rationality that
underlies much of efficient market theory. They point to the frequency with speculative bubbles have
formed in financial markers, as investors buy into fads or get-rich-quick
schemes, and the crashes with these bubbles have ended, and suggest that there
is nothing to prevent the recurrence of this phenomenon in today's financial
markets. In fact, the evidence on price patterns, in the short and long term,
in different calendar months and on different weekdays suggests that there is
much about markets that we cannot explain with a rational investor model. In
this section, we will begin by considering some of the evidence accumulated by
psychologists on human behavior and then consider financial market phenomena
that seem more consistent with an irrational market than an rational one.
Psychological Studies
At
the risk of stating the obvious, investors are human and it is not surprising
that financial markets reflect human frailties. In an extraordinary book (at
least for an academic economist), Robert Schiller presented some of the
evidence accumulated of human behavior by psychologists that may help us
understand financial market behavior. He categorizes these findings into
several areas:
The Need for Anchors
When
confronted with decisions, it is human nature to begin with the familiar and
use it to make judgments. Kahnemann and Tversky, whose research has helped
illuminate much of what is called behavioral finance, ran an experiment where
they used a wheel of fortune with numbers from 1 to 100 to illustrate this
point. With a group of subjects, they spun the wheel to get a number and then
asked the subjects numerical questions about obscure percentages Ð the percent
of the ancient Egyptians who ate meat, for instance. The subjects would have to
guess whether the right answer was higher or lower than the number on the wheel
and then provide an estimate of the actual number. They found that the answer
given by subjects was consistently influenced by the outcome of the wheel spin.
Thus, if the number on the wheel was 10, the answer was more likely to be 15 or
20%, whereas if the number on the wheel was 60%, it was more likely to be 45 or
50. Shiller argues that market prices provide a similar anchor with publicly
traded assets. Thus, an investor asked to estimate the value of a share is
likely to be influenced by the market price, with the value increasing as the
market price rises.
The Power of the Story
For
better or worse, human actions tend to be based not on quantitative factors but
on story telling. People tend to look for simple reasons for their decisions,
and will often base their decision on whether these reasons exist. In a study
of this phenomenon, Shafir, Simonson and Tversky gave subjects a choice on
which parent they would choose for sole custody of a child. One parent was
described as average in every aspect of behavior and standing whereas the other
was described more completely with both positive (very close relationship with
child, above-average income) and negative characteristics (health problems,
travels a lot). Of the subjects studied, 64% picked the second. Another group
of subjects was given the same choice but asked which one they would deny
custody to. That group also picked the second parent. While the results seem
inconsistent Ð the first group chose the second parent as the custodian and the
second group rejected the same parent, given the same facts Ð they suggest that
investors are more comfortable with investment decisions that can be justified
with a strong story than one without.
Overconfidence and Intuitive Thinking
As you have undoubtedly become aware from your
interactions with friends, relatives and even strangers over time, human beings
tend to be opinionated about things they are not well informed on and to make
decisions based upon these opinions. In an illustrative study, Fischhhof, Slovic
and Lichtenstein asked people factual questions, and found that people gave an
answer and consistently overestimated the probability that they are right. In
fact, they were right only about 80% of the time that they thought they were. What
are the sources of this overconfidence? One might just be evolutionary. The
confidence, often in the
face of poor odds, may have been what allowed us to survive and dominate as a
species. The other may be more psychological. Human beings seem to have a
propensity to hindsight bias, i.e., they observe what happens and act as it
they knew it was coming all the time. Thus, you have investors that claim to
have seen the crash in dot.com companies in the late 1990s coming during
earlier years, thought nothing in their behavior suggests that they did.
Herd Behavior
The
tendency of human beings to be swayed by crowds has been long documented and
used by tyrants over time to impose their will on us. In a fascinating
experiment, Asch illustrated this by putting a subject into a group of people,
asking them a question to which the answer was obvious and then inducing other people
in the group to provide the wrong answer deliberately. Asch noted that the
subject changed his answer one-third of the time to reflect the incorrect
answer given in the group. While Asch attributed this to peer pressure,
subsequent studies found the same phenomenon even when the subject could not
see or interact with others in the group. This would suggest that the desire to
be part of the crowd is due to more than peer pressure.
While
there is a tendency to describe herd behavior as irrational, it is worth noting
that you can have the same phenomena occur in perfectly rational markets
through a process called information cascade. Schiller provides an example with
two restaurants, where people come into town one after another. Assume that the
first person to come in picks the first restaurant and assume that the choice
is random. The second person who comes into town will observe the first person
sitting in the first restaurant, and is more likely to pick the same
restaurant. As the number of subjects entering the market increases, you are
likely to see the crowd at the first restaurant pick up, while business at the
second restaurant will be minimal. Thus, a random choice by the first customer
in the market creates enough momentum to make it the dominant restaurant. All
to often, in investing, investors at early stages in the process (initial
public offering) pile into specific initial public offerings and push their
prices up. Other initial public offerings are ignored and languish at low
prices. It is entirely possible that the first group of stocks will be
overvalued, while the latter are undervalued. Since herd behavior is made worse
by rumors by the spreading of rumors, you could argue that the coming together
of the available data and media sites such as CNBC and MSNBC has made it more
possible for herd behavior to spend and not less.
Unwillingness to admit mistakes
It
may be human to err, but it is also human to claim not to err. In other words,
we are much more willing to claim our successes than we are willing to face up
to our failures. Kahneman and Tversky, in their experiments on human behavior,
noticed that subjects when presented with choices relative to the status quo
often made choices based upon unrealistic expectations. They noted that a
person who has not made peace with his losses is likely to accept gambles that
would otherwise be unacceptable to him. Anyone who has visited a casino will
attest to this finding.
In investing, Shefrin and Statman
call this the disposition effect, i.e, the tendency to hold on to losers too
long and to sell winners too soon.[1]
They argue that it is widespread and can cause systematic mispricing of some
stocks. Terrance Odean used the trading records of over 10000 customers at a
discount brokerage house to examine whether there is evidence of this behavior
among investors.[2] He notes
that investors realized only 9.8% of their losses each year, whereas they
realize 14.8% of their gains.[3]
He also finds that investors seem to sell winners too soon, since winning stocks
that get sold continue to go up for months after the sale. Overall, he argues
that there is evidence of the disposition effect among investors.
Empirical Evidence
While
it is evident that human beings do not always behave rationally, it does not
necessarily follow that markets will also be irrational. In fact, you could
argue (as some believers in market efficiency do) that markets can be efficient
even with irrational investors. First, it is possible that there is a selection
process that occurs in markets where irrational investors lose consistently to
rational investors and eventually get pushed out of the market. Second, it is
also possible that irrationalities cut in both directions Ð some leading
investors to buy when they should not and others leading them to sell when they
should not; if these actions offset each other, you could still have a market
price that is unaffected by rational investors. The only way to resolve this debate is to look at the
empirical evidence on the presence or absence of irrationality in market
behavior. In this section, we will begin by looking at experimental studies
that claim to document irrational investors, and then consider the evidence
accumulated through the centuries on bubbles and whether their existence alone
indicates irrational investors. In fact, this is a discussion we will revisit
in the chapters to come, since investment philosophies are based upon specific
(and often contradictory) views of human irrationality.
Experimental Studies
One
of the problems we face when we test for irrationality in financial markets is
the number of variables that cannot be controlled for. Investors enter and
leave markets, new information arrives constantly and the macroeconomic
environment changes frequently, making it impossible to construct a controlled
experiment. A few researchers have attempted to get around this problem by
constructing experimental studies, similar to those used by psychologists and
sociologists in the previous section, to examine how investors behave in
financial markets.
One such study was done at the
University of Arizona. In this study, groups of students were chosen as
subjects and asked to play the role of traders in a single asset for 15 trading
days. They were told at the start of the experiment that a payout would be
declared on this asset after each trading day, and that it would take one of
four values- 0, 8, 28 or 60 cents Ð
with equal probability. Consider how a rational investor would value this very
simple asset. Since the average payout is 24 cents, the asset's expected value
on the first trading day of a fifteen day experiment should be $3.60 (24*15),
the second day should be $3.36 and so on. The traders were allowed to trade
each day and the entire experiment was repeated 60 times. The resulting market
prices each day, averaged across all 60 experiments, are reported in figure
7.10 and contrasted with the expected values to a rational investor.
Figure 7.10: Prices from Behavioral Experiment
There
is clear evidence here of a 'speculative bubble'
forming during periods 3 to 5, where prices exceed expected values
significantly, The bubble ultimately
bursts, and prices approach the expected value by the end of the 15th
period.[4] Furthermore,
when price curbs of 15 cents were introduced, the booms lasted even longer
because traders knew that prices would not fall by more than 15 cents in a
period. Thus, the notion that price limits can control speculative bubbles
seems misguided. Does this
experiment conclusively prove that investors are irrational? Of course not. It
is worth noting, though, that it bubbles are feasible in as simple a market as
this one, where every investor obtains the same information, it is clearly
feasible in real financial markets, where there is much more differential
information and much greater uncertainty about expected value.
In
fairness, it should be noted that the evidence from other experimental studies
is largely supportive of rationality. Investors do seem to make reasonable
judgments based upon the information they have, and markets do a good job of
aggregating this information in the market price.