Evaluating Crime Prevention Scheme Success: Estimating 'Outcomes' or How Many Crimes Were Prevented

Research demonstrates that certain crime prevention techniques work. Accordingly, current evaluations focus on what works and where. One of the key elements in assessing crime prevention success is determining the number of crimes prevented. This allows the cost-effectiveness of schemes to be assessed and different schemes to be meaningfully compared. Evaluation studies of what works include a variety of different approaches, some more robust than others. The current article presents two methods for calculating the outcomes of crime prevention interventions. The basic principle behind both approaches involves subtracting the observed number of crimes from an estimate of the number of crimes that would have occurred had the scheme not existed. Importantly, it is acknowledged that area crime rates are influenced both by general trends and more random factors. Thus, each approach produces a range of estimates to attempt to assess the impact of more random influences.