There are many possible methods of reducing crime (see e.g. Tonry & Farrington, 1995). There is criminal justice or correctional prevention, which involves deterrence, incapacitation and rehabilitation. There is community prevention, which involves targeting community risk factors and social conditions, such as community cohesiveness or disorganization, or using the community as the context for intervention. There is situational prevention, which involves reducing opportunities for offending or increasing the risks of being caught in the physical environment, for example by using closed-circuit television (CCTV) cameras or improved street lighting. And there is developmental or risk-focussed prevention, which involves targeting early child or family risk factors for offending, and enhancing protective factors.How can governmental and other policymakers decide which of these approaches is best? For example, should there be more imprisonment? More police? More rehabilitative programmes in prison or on probation? More community penalties or community programmes? More situational crime prevention? Or more developmental crime prevention?One obvious criterion for the success of a crime prevention programme is the extent to which it reduces crime.However, this cannot be the only consideration. Our argument is that, in choosing between programmes, it is important to consider all their monetary costs and benefits, and to choose the programmes with the greatest benefit-to-cost ratios. Knowledge about value for money is also vital in trying to improve evidence-based crime prevention policy and practice. We need to know what works (and for whom) and what saves money.
THE IMPORTANCE OF COST-BENEFIT ANALYSES FOR GOVERNMENTSIn general, government policymakers do not understand effect sizes such as Cohen's d and think that a 5% absolute decrease in conviction rates is very small. However, they do understand money in and money out.They are impressed by evidence suggesting that, for example, £5 is saved for every £1 spent on a programme, even if the savings are in the future. For example, in 1997 we were invited to go to London to HM Treasury to brief senior officials on cost-benefit analyses of crime prevention programmes (see .Under the recently elected government of Prime Minister Tony Blair, the Treasury was spearheading an ambitious Comprehensive Spending Review, to review public expenditure across all areas of government.After our meeting, the Treasury's involvement was a major factor in launching the government's ambitious Crime Reduction Programme, which had an unprecedented level of funding of £250 million (see Dhiri et al., 2001). CrimRxiv The Importance of Cost-Bene t Analysis of Crime Reduction Programmes 3 As another example, David Farrington and Leena Augimeri met with the Deputy Minister and Assistant Deputy Minister of Public Safety Canada in November 2013 and briefed them about cost-benefit analysis and the SNAP (Stop Now And Plan; see later) early developmental prevention programme