Thought Contagions in the Stock Market

The evolutionary epidemiology of ideas, or thought contagion theory, is introduced and applied to possible examples in the stock market. It is suggested that differences in transmissivity, receptivity, and longevity of belief may contribute numerous irrational influences on the stock market, generating sources of inefficiency. These include a wide variety of mechanisms that may generate both positive and negative market overreactions. The soaring prices of Internet stocks during 1998-1999 are used as an example of how investment ideas correlating with new communication behaviors may affect share prices, and how contagion effects in general can affect the broader market. New avenues of empirical investigation are proposed to test the types of hypotheses presented.