According to the sociologist Georg Simmel, what can you use to predict the behavior of members of a social group?

the answer is: the number of people in the group

Simmel believed that if the group has a small number, the behaviors among the members would be more similar because each members can observe the behaviors of all other members and make a judgement for them.

On the other hand, group with large members tend to have different set of behaviors because it is impossible for them to pay attention to all group members.