Body movements, autonomic arousal, and electroencephalograms (EEGs) of group members are often coordinated or synchronized with those of other group members. Linear and nonlinear measures of synchronization have been developed for pairs of individuals, but little work has been done on measures of synchronization for groups. We define a new synchronization coefficient, S_E, for a group based on pairwise correlations in time series data and employing the notions of a group driver, who most drives the group’s responses, and empath, who is most driven by the group. S_E is developed here in the context of emotional synchronization based on galvanic skin response time series. A simulation study explores its properties, the balance between strong versus weak autocorrelational effects, transfer, group size, and direct versus oscillatory functions. Distributions of S_E are not affected by group size up to 16 members. Norms for interpreting the coefficient are presented along with directions for new research.