OXFORD, England, April 16 (UPI) -- There is no evidence after-school clubs or cognitive-behavioral interventions can prevent youth age 7 to 16 from joining a gang, a British review said.

It's estimated there are some 24,000 U.S. gangs with 760,000 members and internationally street gangs have been identified in developed and developing countries in South America, Europe, Asia and Africa.

Lead researcher, Dr. Paul Montgomery of the Centre for Evidence-based Intervention at the University of Oxford, in England, and colleagues reviewed 2,696 publications relating to youth gangs, but they were unable to find any randomized-controlled trials or quasi-randomized controlled trials on the two main theories to prevent gang membership.

One review examined whether providing opportunities such as after-school clubs prevented gang membership and the other review examined if cognitive-behavioral interventions can keep young people from joining gangs.

The findings, published in the Cochrane Library, said there was no real evidence to back either of these two theories.

"This lack of research is surprising given the scale of the problem," Montgomery said in a statement. "There is an urgent need to rigorously evaluate the various gang prevention strategies that people suggest and try to implement."