In a market consisting of human beings, it seems logical that explanations rooted in human and social psychology would hold great promise in advancing our understanding of stock market behaviour. More recent research has attempted to explain the persistence of anomalies by adopting a psychological perspective. Evidence in the psychology literature reveals that individuals have limited information processing capabilities, exhibit systematic bias in processing information, are prone to making mistakes, and often tend to rely on the opinion of others.
The literature on cognitive psychology provides a promising framework for analysing investors’ behaviour in the stock market. By dropping the stringent assumption of rationality in conventional models, it might be possible to explain some of the persistent anomalous findings. For example, the observation of overreaction of the markets to news is consistent with the finding that people, in general, tend to overreact to new information. Also, people often allow their decision to be guided by irrelevant points of reference, a phenomenon called “anchoring and adjustment”.
Experts propose an alternate model of stock prices that recognizes the influence of social psychology. They attribute the movements in stock prices to social movements. Since there is no objective evidence on which to base their predictions of stock prices, it is suggested that the final opinion of individual investors may largely reflect the opinion of a larger group. Thus, excessive volatility in the stock market is often caused by social “fads” which may have very little rational or logical explanation.
There have been many studies that have documented long-term historical phenomena in securities markets that contradict the efficient market hypothesis and cannot be captured plausibly in models based on perfect investor rationality. Behavioural finance attempts to fill that void. You can read more about efficient market hypothesis here which will further amplify on the subject.
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