In groups, synchronization of movement has been shown to increase conformity, cooperation and trust. Military step has long been used for these purposes but more research on group synchronization is needed to determine its effects on the group as a whole and on individuals within a group. In dyads, groups of two people, synchronization has been demonstrated to increase affiliation, self-esteem, compassion and altruistic behaviour and increase rapport. During arguments, synchrony between the arguing pair has been noted to decrease, however it is not clear whether this is due to the change in emotion or other factors. There is evidence to show that movement synchronization requires other people to cause its beneficial effects, as the effect on affiliation does not occur when one of the dyad is synchronizing their movements to something outside the dyad. This is known as interpersonal synchrony.