 More recent studies have focused on trends which are caused by the rapid increase in prison population since the 1970s, such as the prominence of prison gangs.In his literature review and analysis of evidence about gangs in the California correctional complex, David Sharbek found that gangs formed as a response to a lack of protection from prison officials.According to his research, male prison populations rely on non-structured social norms and on formalized organizations to govern themselves.