The similarity of states: Using S to compute dyadic interest similarity

Several leading international relations theories argue that the degree of interest similarity is an important determinant of dyadic conflict and cooperation. Empirical scholars have long wrestled with operationalizing and measuring this central, yet elusive, concept. Signorino and Ritter's (1999) S algorithm, combined with multiple data sources, provides an attractive solution to this problem. To date, however many scholars have failed to take full advantage of this solution. In this research note we examine the properties of S via simulation and with real data sources, highlighting its virtues and potential limitations. In particular we stress the need to include multiple data sources in the computation and provide scholars with an easy-to-use tool to greatly simplify this task.