Shaw and McKay (1931) initiated a series of studies to determine the factual character of delinquency, primarily how it was distributed geographically in Chicago. They concluded that the social conditions that made a neighborhood the entry point for low-income groups unfamiliar with urban ways led to the breakdown of traditional social controls ('social disorganization'). Shaw and McKay's empirical findings have held up over the years, but some researchers have questioned their depiction of gang life and how delinquent traditions become diffused. A paper by Sykes and Matza (1957) led to a resurgence of scholarly concern regarding social-control perspectives. Sykes and Matza argued that delinquents do not have values antithetical to dominant middle-class norms; on the contrary, their values reflect middle-class standards. Delinquency is based on an extension of defenses to crime in the form of justifications that are considered valid by the delinquent ('neutralization' theory). Hirschi's research (1969) redirected students of delinquency back to the problems of social control that preoccupied Shaw and McKay. Whereas Shaw and McKay's theory suggested how institutional controls operated to encourage compliance, Hirschi examined the same relationships from a social-psychological perspective. The independent variable Hirschi used to explain variations in delinquency was the bond to the conventional order.