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.
Evidence brief: Alcohol and Drug Treatment [PDF, 273 KB]
Evidence brief: Cognitive Behavioural Therapy [PDF, 305 KB]
Evidence brief: Restorative Justice [PDF, 317 KB]
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.
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