Van Kampen's expansion approach in an opinion formation model
  We analyze a simple opinion formation model consisting of two parties, A and B, and a group I, of undecided agents. We assume that the supporters of parties A and B do not interact among them, but only interact through the group I, and that there is a nonzero probability of a spontaneous change of opinion (A->I, B->I). From the master equation, and via van Kampen's Omega-expansion approach, we have obtained the "macroscopic" evolution equation, as well as the Fokker-Planck equation governing the fluctuations around the deterministic behavior. Within the same approach, we have also obtained information about the typical relaxation behavior of small perturbations. 
M.S. de la Lama (IFCA), I.G. Szendro (IFCA), J.R. Iglesias (IF-Ufrgs)   and H.S. Wio (IFCA and Cab)