Chapter 7
The Stock Market,
The Theory of
Rational Expectations,
and the Efficient
Market Hypothesis
Computing the Price of Common Stock
• Basic Principle of Finance
Value of Investment = Present Value of Future Cash Flows
• One-Period Valuation Model
Div1
P1
P0 

(1  ke ) (1  ke )
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(1)
7-2
Generalized Dividend Valuation Model
D1
D2
P0 


1
2
(1  ke ) (1  ke )
Dn
Pn


n
(1  ke ) (1  ke ) n
(2)
• Since last term of the equation is small, Equation 2
can be written as

Dt
P0  
t
(1

k
)
t 1
e
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(3)
7-3
Gordon Growth Model
• Assuming dividend growth is constant, Equation 3
can be written as
D0  (1  g )1 D0  (1  g ) 2
P0 


1
2
(1  ke )
(1  ke )
D0  (1  g ) 
(4)


(1  ke )
• Assuming the growth rate is less than the required
return on equity, Equation 4 can be written as
D0  (1  g )
D1
P0 

( ke  g )
( ke  g )
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7-4
How the Market Sets Prices
• The price is set by the buyer willing to pay the
highest price
• The market price will be set by the buyer who can
take best advantage of the asset
• Superior information about an asset can increase
its value by reducing its perceived risk
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7-5
How the Market Sets Prices
• Information is important for individuals to value
each asset.
• When new information is released about a firm,
expectations and prices change.
• Market participants constantly receive information
and revise their expectations, so stock prices
change frequently.
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7-6
Adaptive Expectations
• Expectations are formed from past experience
only.
• Changes in expectations will occur slowly over
time as data changes.
• However, people use more than just past data to
form their expectations and sometimes change
their expectations quickly.
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7-7
Theory of Rational Expectations
• Expectations will be identical to optimal forecasts using all
available information
• Even though a rational expectation equals the optimal forecast
using all available information, a prediction based on it may not
always be perfectly accurate
– It takes too much effort to make the expectation the best guess possible
– Best guess will not be accurate because predictor is unaware of some
relevant information
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7-8
Implications
• If there is a change in the way a variable moves,
the way in which expectations of the variable are
formed will change as well
– Changes in the conduct of monetary policy (e.g. target
the federal funds rate)
• The forecast errors of expectations will, on
average, be zero and cannot be predicted ahead of
time.
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7-9
Efficient Markets
• Current prices in a financial market will be set so
that the optimal forecast of a security’s return
using all available information equals the
security’s equilibrium return
• In an efficient market, a security’s price fully
reflects all available information
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7-10
Evidence on Efficient Markets Hypothesis
Favorable Evidence
1. Stock prices reflect publicly available information: anticipated announcements
don’t affect stock price
2. Stock prices and exchange rates close to random walk
If predictions of P big, Rof > R*  predictions of P small
Unfavorable Evidence
1. Small-firm effect: small firms have abnormally high returns
2. January effect: high returns in January
3. Market overreaction
4. New information is not always immediately incorporated into stock prices
Overview
Reasonable starting point but not whole story
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7-11
Application Investing in the Stock
Market
• Recommendations from investment advisors
cannot help us outperform the market
• A hot tip is probably information already
contained in the price of the stock
• Stock prices respond to announcements only when
the information is new and unexpected
• A “buy and hold” strategy is the most sensible
strategy for the small investor
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7-12
Behavioral Finance
• The lack of short selling (causing
over-priced stocks) may be explained by loss
aversion
• The large trading volume may be explained by
investor overconfidence
• Stock market bubbles may be explained by
overconfidence and social contagion
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7-13