A report by the University of Sheffield shows that the experience of "restorative justice", in which offenders confront their crime victims, reduces the frequency of reconviction by an average of 27%.
The findings follow an independent evaluation of seven Cambridge University-led experiments in restorative justice. They will be presented to the Cambridge Conference on Evidence-Based Policing on Tuesday 01 July, by Professor Joanna Shapland, Director of the University of Sheffield's Centre for Criminological Research, who led the evaluation team.
The Sheffield report includes seven experiments designed and directed by the Wolfson Professor of Criminology at Cambridge, Lawrence Sherman, and his co-director Dr Heather Strang, who directs the Centre for Restorative Justice at the Australian National University.
The experiments began in 2001 and were conducted in collaboration with the Justice Research Consortium, under the chairmanship of Sir Charles Pollard, former Chief Constable of Thames Valley Police and former Chairman of the Youth Justice Board for England and Wales.
The experiments compared almost 400 cases where offenders had attended restorative justice conferences to some 400 cases where they had not.
During the conferences offenders listened to victims describe the harm the crimes had caused. Each conference lasted from one to three hours, often in prison settings. Victims found the process helpful and positive, while some offenders have described the meetings as "traumatic", as well as life-changing.
The report estimates that 9 of costs to victims and the criminal justice system was saved for every 1 spent on delivering these conferences.
The study examined whether offenders within the restorative justice group were reconvicted within a two-year period. It also shows the percentage by which the rate of reconviction within that period fell among different types of criminal in different parts of the country following the restorative justice programme.
The rate of reconviction for violent offenders sentenced to supervision by the Probation Service under a community sentence in Thames Valley, for example, fell by 55%. The rate of reconviction among career burglars in London fell by 15.5%.
The report notes that while the results of each experiment were uncertain if taken in isolation, the likelihood of the pattern of reductions in the frequency of crime for the seven Cambridge-led tests having occurred by chance was one in 100. These results show consistent benefits across many different stages of the criminal justice process.
The Cambridge experiments included almost 800 cases in which both offenders and victims consented to be randomly assigned to restorative justice.
The calculations of the crime reduction effect are based on comparisons of the restorative justice and control group cases. Professor Shapland found similar results from two other pilots, led by the organisations REMEDI and CONNECT, but these tests were not based on the randomized trials design.
Professor Shapland said: "While the experiments did not show that offenders receiving restorative justice were more likely to stop offending completely, we found that offenders committed less crime overall because they slowed down their rate of offending and reduced the overall cost of the crimes they committed."
Sir Charles Pollard said: "These results leave little doubt that restorative justice is both effective and cost-effective at preventing crime. Since 75% of all convictions in England and Wales are reconvictions of repeat offenders, in principle we could see restorative justice reduce crime substantially across the country."
Professor Sherman said: "These results now mean that 10 out of 12 tests of restorative justice have reduced the frequency of repeat offending in the UK, US and Australia.
"As the results from the Thames Valley Probation experiment show, restorative justice may be especially useful for violent offenders coming out of prison if they are willing to meet their victims and work out an accommodation. Our own evidence shows that restorative justice reduced victim desire for revenge in eight out of eight tests in Australia and the UK, and the Sheffield report shows 33% less repeat offending among offenders coming out of prison after restorative justice than without it."