We want to invest where it will make the biggest difference, so we need to know what works to reduce crime. Evidence Briefs summarise the evidence about how well an investment reduces crime, how much is spent on it, and whether there is scope to increase the level of investment.
Each Evidence Brief is overseen by a research committee chaired by the Justice Sector Science advisor, Associate Professor Ian Lambie. This ensures that the briefs fairly reflect the evidence.
Evidence Briefs are designed as general reference documents rather than advice to support a particular funding decision. Although the Evidence Briefs focus on crime, many of the investments covered will be designed to do more than reduce crime. There will always be broader issues to consider when taking an investment decision such as cultural values, fairness and equity, and societal benefits.
Therapeutic interventions such as counselling aim to reduce the long-term effects of intimate partner violence (IPV) on victims
There is very promising evidence that therapeutic interventions for IPV victims are effective in reducing victims’ vulnerability
Therapeutic interventions for IPV victims are more effective when they are provided for individuals rather than group programmes and when they are tailored to the needs of IPV victims
Each Evidence Brief is designed to advise decision makers on how confident they can be that investment will reduce crime, based on the strength of the evidence. Each Evidence Brief provides an evidence rating based on the same objective criteria. The final rating is built around two separate assessments, one reflecting international evidence, and another – New Zealand evidence.
This approach reflects that effective programmes in one country often, but not always, work in other countries. Therefore, even if international research shows that an investment type can reduce offending, it may not be a strong investment option unless we are able to replicate the results in New Zealand’s crime environment.
Both international and New Zealand evidence is assessed using the Maryland Scale of Scientific Methods, a 5-point scale with randomised controlled trials at the top (level 5) of the scale. At lower levels, there is an increasing risk that findings are subject to selection bias and a wide range of other challenges to validity. The academics who developed the scale consider Level 3 the minimum in order to conclude the intervention reduces crime¹.
The final rating is measured in a six-grade scale varying from “poor” evidence to “very strong” evidence.
New Zealand studies
At least one level 4 or 5 study finds a statistically significant negative impact, no conflicting L4+ studies
Studies show conflicting results, or no impact, or no level 3+ study exists
At least one level 3 study finds a statistically significant positive impact, no conflicting L3+ studies
At least one level 4 study finds a statistically significant positive impact, no conflicting L4+ studies
At least one level 5 study find a statistically significant positive impact, no conflicting L5 studies
International studies
Meta-analysis/systematic review of 5+ studies finds a statistically significant positive impact, no conflicts
Fair (promising)
Very promising
Strong
Strong
Very strong
MA/SR with fewer than 5 studies finds positive impact, or no MA/SR exists and level 4 or 5 studies find a positive impact
Speculative
Fair (promising)
Fair (promising)
Very promising
Strong
MA/SR find conflicting results
Speculative
Speculative
Fair (promising)
Very promising
Strong
MA/SR shows no impact, or no MA/SR exists
Poor
Speculative
Fair (promising)
Very promising
Strong
MA/SR shows negative impact, no conflicting results
Poor
Poor
Speculative
Fair (promising)
Strong
There is also a standard interpretation for each evidence rating, as summarised in the following table.
Investment category
Interpretation
Very strong
Very robust international and local evidence that investment tends to reduce crime.
Investment likely to generate a return if implemented well.
Simple monitoring approach should confirm the investment is providing a positive return.
Little additional evaluation required.
Strong
Robust international and local evidence that investment tends to reduce crime.
Investment likely to generate a return if implemented well.
Could benefit from additional evaluation to confirm investment is delivering a positive return and to support fine-tuning of the investment design.
Very promising
Robust international or local evidence that investment tends to reduce crime.
Investment may well generate a return if implemented well.
Further evaluation desirable to confirm investment is delivering a positive return and to support fine-tuning of the investment design.
Fair/promising
Some evidence that investment can reduce crime.
Uncertain whether investment will generate return even if implemented well.
May be unproven in New Zealand or be subject to conflicting research.
May benefit from trial approaches with a research and development focus.
Robust evaluation needed to confirm investment is delivering a positive return and to aid in detailed service design.
Speculative
Little or conflicting evidence that investment can reduce crime.
Highly uncertain whether investment will generate return even if implemented well.
Primarily suited to trial approaches with a strong research and development focus.
Full rollout should be subject to high-quality evaluation to ensure investment is delivering a positive return, and to deliver insights into detailed service design questions.
Poor
Robust evidence that investment does not reduce crime or that it increases crime.
Should be priority for divestment.
¹ Sherman, L., Farrington, D., Welsh, B., & Mackenzie, D. (Eds). (2002). Evidence-Based Crime Prevention. New York: Routledge