Abstract
In many cases, the refutation against rumor fails to stop its spreading. Instead, the “story” which explains the rumor is often made more imaginative by the refutation itself. It tends to be associated with conspiracy. In this study we tackle this problem mathematically by means of a game of incomplete information. We discuss about the elements that affect rumormongering and adopt three kinds of factors : uncertainty, mental tension, and credulity. And we define the rumor believer's payoff brought by transmitting rumor, considering about its two dimension, “preference” and “value”. Then we analize the mathematical model applying these three factors and two dimensions of believer's payoff. As the result of analysis, we have several conditions on which the refutation is effective. Most of them are trivial, but we get an interesting one. This condition is concerned not with the character of rumor itself or information for refutation, but with the value of the game between refuter and believer of rumor. It is that the believer's risk with communicating the rumor to others is higher while the rumor is false (the refutation is right). On the contrary, if the thematic importance of the rumor is higher while the rumor is true, people continue rumormongering. It explains the intimacy of rumor with conspiracy.
