The interventions were most effective among the young men who reported the highest level of anti-social behaviours.
Spending $500 for therapy and a small cash payment helped reduce crime and violence by half among some of the most troubled young men in West Africa, a new study has found.
Researchers including from the University of Exeter Business School followed nearly 1,000 criminally involved young men who were part of the Sustainable Transformation of Youth in Liberia programme, an 8-week CBT intervention in West Africa that took place between 2009 and 2011.
The study, which is published as a National Bureau of Economic Research working paper and is not yet peer-reviewed, found that a combination of cognitive behavioural therapy (CBT) and economic assistance produced a dramatic reduction in drug-dealing, theft and robbery over 10 years, with almost 350 fewer crimes committed per participant.
Each participant was assigned to a group: the first group received eight weeks of low-cost therapy; in another group the men each received a $200 cash grant; the third group received both the therapy and cash and there was also a control group.
After around 10 years, the researchers carried out a survey among the men and found that therapy when combined with economic assistance produced dramatic reductions in anti-social behaviours, with more than a 50% reduction in self-reported drug-selling, thefts and robberies.
The researchers believe the results show that highly-targeted CBT plus economic assistance could be an inexpensive and effective way to prevent violence, and provide an alternative to aggressive policing, incarceration and other coercive tools to tackle social problems.
Together, the two interventions cost $530 to deliver and the researchers estimate that therapy plus cash led to roughly 34 fewer thefts and robberies per year per subject.
Over 10 years it meant 338 fewer crimes committed per participant with each crime avoided for a cost of around $1.50.
The researchers also found that the interventions were most effective among the young men who reported the highest level of anti-social behaviours.
Therapy alone also had a positive effect on crime and violence, but the results were weaker and more variable across the sample.
There was no evidence to suggest that cash alone had any positive effect on crime and violence.
The researchers hypothesise that while the cash will not have increased the participants' earnings for more than a few months, it allowed the young men to start legitimate enterprises and avoid an immediate return to crime while helping to cement their new non-criminal identity and the habit-forming practices learned from CBT.
Julian Jamison, Professor of Economics at the University of Exeter Business School, said: "Cognitive behavioural therapy-informed programs have emerged as one of the most promising alternatives to policing and incarceration.
"What has been unclear, however, is whether the effects of therapy are lasting.
"Our results suggest instead that behaviour changes can be lasting, especially when therapy is combined with even temporary economic assistance. The results also suggest that there are high returns to targeting the most violent and antisocial young men.
"The psychological theory underlying CBT suggests a plausible hypothesis as to why: receiving cash was akin to an extension of therapy, in that it provided more time for the men to practise independently and to reinforce their changed skills, identity, and behaviours.
"The therapy helped participants change their intentions, identity and behaviour, and provided almost daily commitment and reinforcement. In this way, the grant may have parallels to "booster sessions" commonly used in therapy."
Cognitive behaviour therapy reduces crime and violence over 10 years: Experimental evidence by Christopher Blattman, Sebastian Chaskel, Julian C. Jamison, and Margaret Sheridan is published as a National Bureau of Economic Research working paper.
