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Related to market efficiency: Efficient market hypothesis
The extent to which the price of an asset reflects all information available. Economists disagree on how efficient markets are. Followers of the efficient markets theory hold that the market efficiently deals with all information on a given security and reflects it in the price immediately, and that technical analysis, fundamental analysis, and/or any speculative investing based on those methods are useless. On the other hand, the primary observation of behavioral economics holds that investors (and people in general) make decisions on imprecise impressions and beliefs, rather than rational analysis, rendering markets somewhat inefficient to the extent that they are affected by people.
See efficient market.