Market Efficiency Flashcards
Strong Form Effiency
All Relevant Information (private’s and public)
Prices react to new information as soon as it is generated, rather than when it is publicly disclosed. If a market is efficient in strong form it must be efficient in semi strong form and weak form
Semi-strong form efficiency
Public information (current and past)
Prices respond to information disclosure immediately. if a market is efficient in semi strong form it must be efficient in weak form
Weak form efficiency
Past information
Future prices cannot be predicted based on analysis of Past prices
Example of what happens with dividend information in weak form
Current prices have already fully incorporated all historical dividend records
Example of what happens with dividend information in semi strong form
Share prices react to a dividend increase as soon as the decision is announced
Example of what happens with dividend information in strong form
Share prices react to a dividend increase as soon as the decision is made, rather than when the decision is announced to the public
TESTING FOR WFE
if market prices do not follow any predictable patterns
It must follow a random walk
Therefore forecast based on past price patterns are useless
TESTING FOR WFE
if prices follow a random walk
Technical analysis is useless
Technical Analysis?
Past information
Fundamental analysis?
Public information
Private information?
Insider trading
TESTING FOR WFE
See if technical analysis can make abnormal returns
If YES then WFE can be rejected
How does a spread out scatter graph empirically price random walk theory
Correlation between change at T and price change at T+1 is weak
Therefore share price movements follow a random walk, thus further implying that stock markets are efficient in the weak form
TECHNICAL ANALYSIS
forecast stock prices based on watching the fluctuations in historical prices and volume should have no marginal value if the market is
WFE
If there are patterns in the market a few smart investors would profit from these patterns in the short run but once the market recognises the pattern it will disappear
EMPIRICAL EVIDENCE IN WF EMH
tests to support this?
- Tests on aggregate stick indices (ftse 100) support WFE
2. Recent evidence suggests returns from portfolios of small stocks might have some autocorrelations (small firm effect)
EMPIRICAL EVIDENCE IN WF EMH
counter example to weak form of EMH
momentum strategies
Past performers would outperform past losers
Is the expected return for stocks equal to zero in an efficient market?
no. abnormal returns will be 0 as cannot beat the market
the weak form of efficient market theory implies that technical analysis is valuable
no
the small-firm effect is cited as evidence against market efficiency
yes
what happens when fundamental analysts research the value of stocks in ssfe?
this should have no marginal value
who first spoke about event study
fama et al 1969
event study is the corner stone of much research in stock market efficiency
what is event study
abnormal returns (actual return - expected return) around an announcement
how long should the event window be?
long enough to capture the significant effect of an event and at the same time effectively control for the compounding effects.
in the case of confounding events a short event window is preferred
many empirical studies arbitrarily defined their long event windows without further explanation
how do we calculate abnormal return for event study
estimate normal returns
You gather 60 monthly returns for Tesco Corporation and estimate its beta as 1.35 and its alpha as +0.7% per month. Next month both the market and Grecian Urns’s stock price fall by 5%. What is Grecian Urns’s abnormal return?
r^i - (a^i + B^i + r^m)
-0.05(0.007+1.35*(-.05)) = 0.0105 = 1.05%