  What is the effect of the combined direct and indirect social influences-peer
pressure (PP)-on a social groups collective decisions? We present a model that
captures PP as a function of the socio-cultural distance between individuals in
a social group. Using this model and empirical data from 15 real-world social
networks we found that the PP level determines how fast a social group reaches
consensus. More importantly, the levels of PP determine the leaders who can
achieve full control of their social groups. PP can overcome barriers imposed
upon a consensus by the existence of tightly connected communities with local
leaders or the existence of leaders with poor cohesiveness of opinions. A
moderate level of PP is also necessary to explain the rate at which innovations
diffuse through a variety of social groups.
