Question Time: How do convictions vary by region?

by | Dec 18, 2015

I’ve been continuing on my data exploration journey you can read my previous blogs here and here. This week I’ve been using Qlik to look at crime statistics for New Zealand and how conviction rates vary by region and crime. Thank you again Statistics New Zealand for supplying great data to explore. Thanks to New Zealand Ministry of Justice (MoJ) and New Zealand Police for their data too.
The regions are broken down into the MoJ ‘District Court Regions/Areas’, you can read about changes to court services here. The map locations below are indicative and not necessarily the central point for the region. The values are relative to each other.
Conviction Rates by Region - Map
Conviction rates vary from 66.9% in the Wellington region to 81.6% for Taranaki-Wanganui for the 2014/15 Fiscal year. While there are factors that will affect the rate of convictions i.e. population count/density and available resources, it’s a good performance indicator for the region to see how they track nationally.
Conviction Rates by Region Previous Year Comparison
If we exclude the more densely populated areas; Auckland, Wellington and Christchurch, we can see that the North Island has higher conviction rates than areas on the South. However, we can see that Christchurch has a much higher conviction rate than the highly populated areas in the North, we’ll explore that in a bit more detail soon, but first let’s take a look at how NZ prosecutions have been tracking overall.
Convictions vs Total Outcomes All Regions by Year
Overall, prosecution rates remained steady up until 2006 where we see a spike lasting until 2010 with it trailing off to a much lower number in the last couple of years. When compared with the number of crimes reported over the similar periods, the rate of prosecutions tracks against the rate of reported crime, although the periods aren’t identical (fiscal vs calendar year) we can see the trends are similar.
Reported Crimes by Year
With greater populations you’d expect to see more crime, but there seems to be an exception with Canterbury. It has a high conviction rate, 81%, compared to the other NZ regions, specifically the high population areas of Wellington and Auckland. The conviction rate is close to the highest value for the country, with a prosecution rate very similar to that of Wellington for 2014/15. To understand it a bit better, let’s break it down into the types of offence.
Wellington-Canterbury Offence Types Comparison
We can see that Canterbury has a much higher rate of ‘Traffic and Vehicle Regulatory Offences’ convictions. There’s a few potential reasons for this; the Canterbury region may have more available resource allocated to target motoring offences or Canterbury may have better methods for capturing and prosecuting people who commit motoring offences compared to the Wellington region. They may also have a more robust method for capturing the evidence required to secure a conviction.
Overall, it seems Canterbury is very effective at turning prosecutions into convictions. As a highly populated area, it would be good to understand their approach further to see what lessons can learned and then be applied to the rest of NZ. Alternatively Canterbury may be better at assessing which cases to put forward for prosecution which would also be valuable.
One final thought; with a rising population it’s unusual to see crime rates drop, especially with varied conviction rates across the country. It’s possible that crime rates have dropped from factors I haven’t yet investigated. However, it would be interesting to see if there is a genuine reduction in crime or a change in the way the figures are captured and reported.
Keep exploring! Daniel.
Data Source: Statistics New Zealand

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