  We propose the consistent statistical approach for the quantitative
description of simple psychological phenomena using the methods of quantum
theory of open systems (QTOS). Taking as the starting point the K. Lewin's
psychological field theory we show that basic concepts of this theory can be
naturally represented in the language of QTOS. In particular provided that all
stimuli acting on psychological system (that is individual or group of
interest) are known one can associate with these stimuli corresponding
operators and after that to write down the equation for evolution of density
matrix of the relevant open system which allows one to find probabilities of
all possible behavior alternatives. Using the method proposed we consider in
detail simple model describing such interesting psychological phenomena as
cognitive dissonance and the impact of competition among group members on its
unity.

Physics and Society;Quantum Physics