View source for Efficient-Market Hypothesis

'''Malkiel's efficient market hypothesis:'''
"No one can consistently predict either the direction of the stock market or the relative attractiveness of individual stocks, and thus no one can consistently obtain better overall returns than the market.  And while there are undoubtedly profitable trading opportunities that occassionally appear, these are quickly wiped out once they become known.  No one person or institution has yet to produce a long-term, consistent record of finding money-making, risk-adjusted individual stock-trading opportunities, particularly if they pay taxes and incur transaction costs." (pg 246)


-Malkiel's efficient market hypothesis has three versions.

#'''Weak form-''' You can not predict future stock prices on the basis of past stock prices, therefore stock prices behave very much like a random walk.
#'''Semi-strong form-''' You can not even use published information to predict future prices.  No public information will help an analyst select under-valued securities because market prices already include public information such as balance sheets, income statements, and divivends.
#'''Strong form-''' Nothing, not even unpublished developments, can be of use in predicting future prices; everything that is known, or knowable, has already been reflected in the present stock price.  Information contained in past prices or any publicly available information is assimilated into market prices.  These prices adjust so rapidly that if some degree of mispricing exists, it does not persit for long.

'''Example:'''  A student comes across a $100 bill lying on the ground and stops to pick it up.  The professor says, "Don't bother, if it were really a $100 bill, it wouldn't be there."
[[Image:bill.jpg]]
This example illustrates what financial economists, such as Malkiel, mean when they state that '''markets are efficient'''.  $100 bills are not lying around on the ground because markets are so efficient that they do not allow for investors to earn above-average returns without accepting above-average risks.  If predictable patterns are present in the stock market and if market prices are determined by irrational investors, then professional investment managers clearly ought to be able to use them to be able to use them to beat a simple index fund.  However, a large body of evidence suggests that professional investment managers are not able to outperform index funds that simply buy and hold a diversified portfolio.
:::[[Image:four.jpg]]

Richard Roll, an academic economist, agrees with Malkiel's market efficient hypothesis after unsuccessfully investing his own money in theories that supposedly predicted market prices.
"I have attempted to exploit a whole variety of strategies supposedly 



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[[Random Walk]]  |  [[Efficient-Market Hypothesis]]  |  [[Fundamental Analysis]]  |  [[Technical Analysis]]  |  [[Non-Random Walk Theory]]  |  [[Market Efficiency vs. Behavioral Finance]]