The degree of group polarization in making a decision concerning the difficulty of the task to be taken correlates negatively with the efficiency of the group. In its turn the polarization is a direct result of low ability for self-estimation in the group. The polarization also is positively connected with the ability to comprehend the structure and workings of the leadership in the group. Group efficiency in the decision-making is therefore a combined effect of integration of the described social-perceptual phenomena and of proper differentiation of roles in the group under such conditions.