We consider stability of equilibrium points against slight perturbations on the information structures of games from the viewpoint of Selten's concept of perfectness. We give an example in which equilibrium points are not necessarily stable, and provide sufficient conditions for stability. We also point out the difference between our stability and that of Selten's perfect equilibrium point.
This note is based on a part of a Master's Thesis by the author. He is grateful to Prof. Mitsuo Suzuki of Tokyo Institute of Technology and Dr. Mamoru Kaneko of University of Tsukuba for their encouragement and valuable advice.