  A mathematical model for behavioral changes by pair interactions (i.e. due to
direct contact) of individuals is developed. Three kinds of pair interactions
can be distinguished: Imitative processes, avoidance processes, and
compromising processes. Representative solutions of the model for two different
interacting subpopulations are illustrated by computational results.
  The equations of game theory are shown to result for a special case of
imitative processes. Moreover, a stochastic version of game theory is
formulated. It allows the derivation of equations for the most probable or the
expected distribution of behavioral strategies and of (co)variance equations.
The knowledge of the (co)variances is necessary for the calculation of the
reliability of game theoretical descriptions.
  The use and application of the introduced equations is illustrated by
concrete examples. Especially, computational results for the selforganization
of social conventions by competition of two equivalent strategies are
presented.
