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Belief merging and revision under social influence: An explanation for the volatility clustering puzzle

Siddiqi, Hammad (2006): Belief merging and revision under social influence: An explanation for the volatility clustering puzzle.

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Abstract

A share price in a stock market can be thought of as arising out of an aggregation procedure. The price of a stock aggregates many individual beliefs into a collective one, the collective will of the market, so to speak. How does this aggregation come about? And is this aggregation fair in the sense that it correctly reflects the value? Furthermore,in the context of a stock market, it becomes immediately clear that belief merging cannot be separated from belief revision since investors in the market have a direct stake in what others think and clearly find it optimal to revise their beliefs in the light of the information about what others believe. We show that if investors are revising their beliefs not only after receiving new exogenous information but also after their social interactions with other investors and these revised beliefs are getting merged to generate the stock price under the accepted principles of finance (no arbitrage) then the resulting price dynamics explain a long standing puzzle in finance, the volatility clustering puzzle.

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