by Frank Shostak
Mises.org
It is widely held that financial asset prices fully reflect all available and relevant information, and that adjustments to new information is virtually instantaneous. This way of thinking which is known as the Efficient Market Hypothesis (EMH) is closely linked with the modern portfolio theory (MPT), which postulates that market participants are at least as good at price forecasting as any model that a financial market scholar can come up with, given the available information.1
It is held that asset prices respond only to the unexpected part of any information, since the expected part is already embedded in prices. According to MPT, the individual investor cannot outsmart the market by trading based on the available information since the available information is already contained in asset prices.