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Topic four - What works


Evaluation is the last step in any crime problem-solving approach. This final topic highlights the importance of evaluation and how the Campbell Collaboration and EMMIE (and other databases) now provide access to meta evaluations of common crime prevention measures. Some of the debates about the efficacy of such clearinghouses and the different approaches to what constitutes evidence are addressed in additional readings. The objective of this section of this Module will be to introduce the clearinghouses and show how searches can be undertaken to locate relevant studies.


The Campbell Collaboration

The Campbell Collaboration was established by criminologists in the year 2000, to develop an evidence base for crime prevention. The Campbell Collaboration is an international, non-profit research network which prides itself on conducting and publishing high quality systematic reviews of interventions related to crime and justice, education, international development and social welfare (Campbell Collaboration, 2016).

The Campbell Collaboration mission statement is as follows:

The Campbell Collaboration promotes positive social and economic change through the production and use of systematic reviews and other evidence synthesis for evidence-based policy and practice. (Campbell Collaboration, 2018)

Systematic reviews summarize and evaluate the best available research on specific programmes and interventions (Campbell Collaboration, 2018). The results from multiple high-quality studies are synthesized to produce the best possible evidence. Great importance is placed upon the integrity of the process through which systematic reviews are produced. The rigorous process requires the pre-determination of intended search procedures, and clear criteria for inclusion and exclusion of studies. This ensures the transparency and integrity of the review, as other researchers can easily replicate the results.

All eligible studies are screened for quality, and studies with methodological weakness are excluded. Coding for all relevant studies, and analysis, is undertaken and, where possible, a meta-analysis will be conducted. Combining the findings of multiple studies, in this way, has multiple advantages, including mitigating the shortcomings of individual studies; providing insight in cases of conflicting results; and increasing statistical power and the ability to detect effect sizes with greater precision. The estimation of effect sizes is largely dependent on the number of participants in a study, the greater the number, the greater the precision of effect size estimation. Thus, pooling the participants from similar studies will result in increasing the likelihood of more precise effect size estimations, as well as detecting small effects that would have otherwise gone unnoticed in individual studies.

The Campbell Collaboration library has published many systematic reviews, a high proportion of which related to crime prevention interventions. Consistent with the public health model of prevention classification levels, crime prevention activities or interventions can be classified as being primary, secondary or tertiary prevention.

Primary prevention refers to activities aimed at preventing crime on a universal level i.e. crime prevention activities targeted at the entire population. Relevant primary prevention studies include: School-based interventions for reducing disciplinary school exclusion (2018); and Juvenile curfew effects on criminal behaviour and victimisation (2016).

Secondary prevention refers to activities aimed at population groups who have not yet engaged in criminal behaviour but are at risk of doing so. Relevant secondary prevention studies include: Preventive interventions to reduce youth gang violence in low and middle-income countries (2015); and Mentoring interventions to affect juvenile delinquency and associated problems (2013).

Tertiary prevention refers to activities aimed at preventing those who have already engaged in criminal activity from future reoffending. Relevant tertiary prevention studies include: Police-initiated diversion for youth to prevent future delinquent behaviour (2018); Sexual offender treatment for reducing recidivism among convicted sex offenders (2017).

Further information about the Campbell Collaboration is provided in the section on Key clearinghouses.



Academics at the University College London have developed the rating and ranking system known as EMMIE. EMMIE stands for the following:


Impact on crime

Whether the evidence suggests the intervention led to an increase, decrease or had no impact on crime.


How it works

What is it about the intervention that could explain its effects?


Where it works

In what circumstances and contexts is the intervention likely to work/not work?


How to do it

What conditions should be considered when implementing an intervention locally?

Economic Cost

How much it costs

What direct or indirect costs are associated with the intervention and is there evidence of cost benefits?

For an introduction to EMMIE, please see Johnson, Tilley and Bowers, 2015

Through the introduction of these additional variables, EMMIE seeks to go beyond what the Campbell Collaboration achieves. By providing some insight into the way an intervention works, the moderating variables, and how much it costs, EMMIE is more helpful in shaping decisions of policymakers than just merely outlining whether or not an initiative works.

The Crime Reduction Toolkit provides an overview of the findings arising from reviews across various forms of crime prevention. Further information about EMMIE and the Crime Reduction Toolkit is provided in the section entitled 'Further resources'.

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