Thus, models of deviance which use causal sequences are useful in formulating and evaluating social policy. Canadian scholars have published a variety of ideas regarding deviance. For example, Clairmont outlined a sequence of events and conditions which resulted in the evolution of the community of Africville, Nova Scotia into a deviance service center. Another study focused on Edmonton, Alberta, and tried to determine the possible impact of community cohesiveness on deviance. In other research, Linden modified control theory to argue that both affective ties toward delinquent peers and the lack of constraints imposed by ties to parents and other elements affect the likelihood of delinquency. Hagan focused on crime in upper social groups. The Opportunities for Youth project in Seattle is an example of an action program based on causal theory. Theories do not necessarily require causal sequences, however. However, stating theories in causal sequences provides certain technical advantages for testing a larger theoretical model, as shown by data regarding delinquency, the mother's employment, and the adequacy of supervision. In several other Canadian studies, causal sequences have been relevant for policymaking. In addition, the Mobilization for Youth Project in New York illustrates the importance of determining the direction of a potential causal link between delinquency and blocked opportunities. References are contained in a bibliography located at the end of the volume and listing about 800 sources.