An investigation into ties between bars, violence and deprivation could help predict trouble-spots for assaults in the future.
A new study by staff at Wellington firm Dot Loves Data found higher numbers of assaults could be linked to bars being clustered and close-by, and to areas with low socio-economic status.
The authors say policymakers seeking to tackle booze-related harm needed to take such factors into account.
To build the picture, they pulled together police crime statistics and data from the Ministry of Justice specifying locations of all alcohol outlets in the country.
The firm also drew on its own Dynamic Deprivation Index (DDI) that each month tracked the socio-economic status of 1896 "area units" – roughly suburb-sized measures that combine the smaller 46,393 "meshblocks" used by Statistics NZ to break down populated areas.
When all of the information was combined, firm managing director and study co-author, Dr Paul Bracewell, said "very clear patterns" began to emerge around the timings and locations of assaults.
The data – all from 2016 – showed there was 20,602 recorded assaults, of which 17,374 could be pinned down to a day, time and location.
They revealed how 17,374 assaults occurred in just 8542 distinct meshblocks - meaning there was a tendency for multiple assaults to occur within the same one.
The team also refined the Ministry of Justice's dataset on pubs and bars to eliminate the possibility of "diffusion bias".
"By definition, with off-licence venues the location of alcohol purchase differs from the location of consumption," he said.
Yet, for on-licenced venues, there was no separation between the location of purchase and consumption - meaning that any alcohol-related violence was more likely to occur within a small vicinity of the venue.
"We were able to accurately geocode the locations of 1412 out of 1510 taverns across New Zealand."
The team were ultimately able to crunch four variables: distance to the nearest bar, the density of bars within a 500m radius, the socio-economic status of area units, and the population density within each of them.
They then investigated how well they all predicted the occurrence of assaults at "peak" times – between 10pm and 3am on weekends – and otherwise in "off-peak" times.
Unsurprisingly, a disproportionate number of assaults happened during peak times – but also within a very short distance of taverns.
"This is disproportional to both the population living within such a distance of taverns - and the land mass covered."
The figures showed a much higher proportion of assault occurred in more deprived areas – and that, in off-peak times, socio-economic status proved a better predictor of assault than the nearness or number of bars.
"The analysis suggests that assaults occurring at peak times are far more likely to be alcohol related whereas assaults occurring at off peak times are more likely to be driven by socio-economic conditions."
Bracewell believed the results could be used to predict where and when peak-time assaults were likely to happen in future, enabling police to co-ordinate resources accordingly.
But as for the rest of the time, reducing the number of assaults was a more difficult challenge.
"Our analysis suggests that off peak assaults are more likely to be driven by socio-economic conditions," Bracewell said.
"Hence, reducing off peak assaults would require the government to address the socio-economic conditions of which assaults are a symptom.
"This is much easier said than done."
Police prevention manager Inspector Paula Holt said the research was not surprising, and previous studies had linked the density of bars to violent crime.
Police worked with liquor licensing inspectors and medical officers of health on strategies using one-way door policies, CCTV and city ambassadors.
The Sale and Supply of Alcohol Act also allowed local councils and communities to develop local alcohol policies, and meant licensing bodies had to look at density, opening hours and nearness to schools and churches when considering applications.
"However, the community itself has a responsibility in contributing to its own safety," Holt said.