Group interaction is an important aspect of human social behavior. During some group events, the activities performed
by each group member continually influence the activities of others. This process of influence can lead to synchronized group activity, or the entrainment of the group. Understanding entrainment is important, because it can be a critical behavioral indicator of group cohesiveness, and can provide context for accurately understanding a group’s affective behavior. In this paper, we present a novel method to automatically detect group psychomotor entrainment, which takes multiple types of discrete, task-level events into consideration. We experimentally validated the method on two synchronous rhythmic activities, “the cup game” and a marching task. We also compared its accuracy against two alternate synchrony detection methods in the literature. The results suggest our method can successfully measure group psychomotor entrainment, and is more accurate compared to other methods. This method will be useful to researchers interested in quantitatively and automatically measuring entrainment, and can also provide insight into understanding how groups interact socially.