Contagion or epidemic models of ﬁnancial markets are proposed in which interest in or attention to individual stocks is spread by word of mouth. The models give alternative interpretations of the random walk character of stock prices. A questionnaire survey of institutional investors was undertaken to ascertain the relevance of such models. Questions elicited what fraction of these investors were unsystematic and allowed themselves to be influenced by word-of-mouth communications or other salient stimuli. Rough indications of the infection rate and removal rate were produced. Investors in stocks whose price had recently increased dramatically to a high P/E ratio were contrasted with a control group of investors.
Shiller, Robert J. and Pound, John, "Survey Evidence on Diffusion of Interest Among Institutional Investors" (1986). Cowles Foundation Discussion Papers. 1037.