Due to inherent limitations in law enforcement data and ethnographic studies, determining the proportion of adolescents and young adults who join street gangs is best accomplished through self-report studies of a specified target population. Based on a national study properly weighted to be representative of all youth, recent research finds that approximately 8 percent of all youth have joined a gang by their twenties. This estimate is also highly dynamic. In a multisite study in cities with known and significant gang problems, the percentage of youth who joined a gang peaked in the early teens and declined precipitously thereafter. These estimates, of course, vary across localities and are highly contingent on the type of gang problem observed in a given community. Studies conducted in some urban cities with long-standing gang problems have found that 15 percent or more of youth joined a gang at some point during their adolescent and youth-adult years.
A common misconception surrounding gangs is that once a person joins, he or she stays in the gang for an extended period of years. By following subjects over time, longitudinal research studies provide the only reliable method to determine the duration in which a person remains in a gang. Based on multiple studies, in multiple cities, across multiple research projects, it is repeatedly found that most youth who join a gang do not remain in it for an extended period of time. For the majority of youth who join a gang, the average amount of time they remain active in the gang is one to two years, and fewer than 1 in 10 gang members report involvement for four or more years. However, the more embedded a person is in a gang—e.g., the more his or her self-identity is derived from the gang—the longer that person will remain in the gang, which negatively impacts efforts at severing gang ties.
In sum, joining a gang is not a rare event, relatively speaking. However, a corollary finding also emerges from these systematic studies: Even in the most gang-ridden areas across the United States, most youth do not join a gang. Comparatively, law enforcement agencies report older, more adult-aged gang members in the New York Gang Study (in 2011, approximately two-thirds were 18 and over), reflecting the tendency of agencies to focus primarily on the more embedded (hard-core) members of gangs. This is especially the case in urban areas with long-standing gang problems, where adult-aged members make up a clear majority; in newer gang-problem areas outside the larger cities, this proportion is noticeably smaller.