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The Old Constant : Human Psychology

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The Old Constant: Human Psychology

According to the Efficient Market Hypothesis, competition will instantaneously cause the effects of new information to be reflected in actual share prices. This assumption presupposes that the participants in a market act rationally. The concept of the homo economicus has a long-standing history in economics and is a relevant premise of efficient markets. According to the founder of economic thought, Adam Smith, the homo economicus is human who constantly peruses self-interest while always acting rational to reach his subjectively defined ends (Coase, 1994). At times, psychologists joined this discussion and challenged the concept of the economic man. Among the most prominent researchers who question the rationality in human decision making is Daniel Kahneman. Kahneman challenged the rationality in decision making processes and is one of the founders of behavioral economics. Behavioral economists argue that markets are not perfectly efficient because various cognitive biases in humans (HBR, 2015). Among the most prominent cognitive biases that influence stock prices are the Overconfidence Hypothesis and the Disposition Effect. The Overconfidence Hypothesis describes the tendency of individual investors to trade excessively based on a mistaken belief that they can pick winners and losers better than investment professionals. Overconfidence is characterized by three main tendencies. First, overconfident investors tend to overreact to

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