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Any test of this proposition faces the joint hypothesis problem, where it is impossible to ever test for market efficiency, since to do so requires the use of a measuring stick against which abnormal returns are compared —one cannot know if the market is efficient if one does not know if a model correctly stipulates the required rate of return.
The joint hypothesis problem is the problem that testing for market efficiency is difficult, or even impossible. Any attempts to test for market (in)efficiency must involve asset pricing models so that there are expected returns to compare to real returns. It is not possible to measure 'abnormal' returns without expected returns predicted by ...
In the 1970s Eugene Fama defined an efficient financial market as "one in which prices always fully reflect available information". [3] Fama identified three levels of market efficiency: 1. Weak-form efficiency. Prices of the securities instantly and fully reflect all information of the past prices. This means future price movements cannot be ...
Peter Lynch, a mutual fund manager at Fidelity Investments, has argued that the random walk hypothesis is contradictory to the efficient market hypothesis-- though both concepts are widely taught in business schools without seeming awareness of a contradiction.
The adaptive market hypothesis, as proposed by Andrew Lo, [1] is an attempt to reconcile economic theories based on the efficient market hypothesis (which implies that markets are efficient) with behavioral economics, by applying the principles of evolution to financial interactions: competition, adaptation, and natural selection. [2]
In an article in the May 1970 issue of the Journal of Finance, entitled "Efficient Capital Markets: A Review of Theory and Empirical Work", [14] Fama proposed two concepts that have been used on efficient markets ever since. First, Fama proposed three types of efficiency: (i) strong-form; (ii) semi-strong form; and (iii) weak efficiency.
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A market can be said to have allocative efficiency if the price of a product that the market is supplying is equal to the marginal value consumers place on it, and equals marginal cost. In other words, when every good or service is produced up to the point where one more unit provides a marginal benefit to consumers less than the marginal cost ...