  We study a model for opinion formation which incorporates three basic
ingredients for the evolution of the opinion held by an individual: imitation,
influence of fashion and randomness. We show that in the absence of fashion,
the model behaves as a bistable system with random jumps between the two stable
states with a distribution of times following Kramer's law. We also demonstrate
the existence of system size stochastic resonance, by which there is an optimal
value for the number of individuals N for which the average opinion follows
better the fashion.
