It is the first time the use of firearms by police in mental health-related events has been researched in New Zealand.
The findings have been published in the International Journal of Law and Psychiatry.
"We extracted data relating to mental health state, demographics, setting, police response, outcome of shooting, and whether the individual was known to police, mental health services, and with a history of mental distress or drug use," the researchers explained in the study.
"Of the 258 reports analysed, 47 (18 per cent) involved mental health-related events compared to 211 (82 per cent) classified as non-mental health events."
Just over 40 per cent of those mental health events resulting in shootings.
And over half of those resulted in fatalities.
"Across all shooting events, a high proportion of individuals possessed a weapon, predominantly either a firearm or a knife, and just under half were known to police and had known substance use," they found.
"Of the 19 mental health events, 47.4 per cent of individuals were known to mental health services and in 89.5 per cent of cases whānau were aware of the individual's mental health distress and/or history [at the time of the event].
"These findings suggest opportunities to prevent the escalation of events to the point where they involve shootings."
Researchers found that the fatal cases predominantly involved young males - but there was not enough information in the IPCA reports to establish any patterns around ethnicity.
"Lack of ethnicity data limits the accountability of the IPCA and is an impediment to informed discussion of police response to people of different ethnicities, and Māori in particular, in New Zealand."
The researchers explained the study came about after armed police responses were "thrust to the forefront of debate locally and internationally following the resurgence of the Black Lives Matter movement".
They said there was also more of an awareness of heightened risk of use of force against Māori and Pasifika peoples, and increased media attention to these issues.
"In this paper, we review use of firearms by police in mental health related events in New Zealand," they said.
"New Zealand has a growing concern regarding the number of police responses to mental health-related events.
"In 2018, police reported that one in 10 people who were suicidal or experiencing mental distress were subjected to use of force by police...use of force represents a continuum of police response including open hand techniques, handcuffs, physical restraint, pepper spray, and Tasers.
"In the 2018/19 year, police received 32,994 mental health-related calls, including 24,662 calls to suicide-related events.
"Recent international studies have also indicated a significant number of incidents involving police use of firearms during interactions with people experiencing mental illness.
"Consistent with the international literature, the vast majority of fatalities by police use of firearms were male, on average in their thirties and occurred in a metropolitan area.
"All but six of the 48 cases had recorded histories with mental health services before the fatal incident occurred.
"Excluding substance use disorders, one-third of the group had been diagnosed with a mental illness. Half of those suffering from co-existing psychotic and substance use disorders had contact with mental health services less than two weeks before their death."
The researchers posed that international research trended toward an "increasing number of police call-outs to individuals experiencing distress who belong to other underrepresented (and discriminated against) minority groups, who are at greater risk of being killed in an encounter with law enforcement".
"The New Zealand Police have acknowledged and responded to the increasing call outs involving people in the community experiencing mental distress," they said.
"Police provides for the use of firearms by police officers to defend themselves or others if they fear death or grievous bodily harm and cannot reasonably protect themselves or others in a less violent manner.
"Research has shown, however, that Māori are disproportionately impacted by a police use of force, often while experiencing mental distress. Māori, who comprise 16.5 per cent of the overall population, are almost eight times more likely than Europeans to be subjected to police use of force.
"Despite international studies reporting that the use of force is more prevalent with people experiencing co-existing mental health and substance use disorders there remains little investigative focus on the use of force by New Zealand police during callouts to mental health-related events.
"No research has explored the use of firearms by the police in mental health-related events.
"This article reports firearm use by police in New Zealand, comparing mental health with non-mental health-related events and investigating the role of ethnicity."
The researchers concluded that people experiencing mental distress in New Zealand were "disproportionately likely to be subject to armed police response and more likely to be killed in armed encounters".
"While individuals subject to fatal police response are likely to be in possession of firearms and are likely to have used substances, these factors do not explain the observed differences in police use of firearms," the study said.
"Police and whanau knowledge of individuals' mental health history suggest opportunities for intervention and negotiation with individuals in crisis.
"Future studies should utilise police databases triangulated with mental health services data to better understand the nature of mental health events involving police."
They also said "greater attention to the relationship between ethnicity and police response" was crucial.
"We argue that all IPCA reports should include demographic information regarding ethnicity to ensure public access to information on police practices in its entirety," the researchers said.
"We found a lack of reporting by the IPCA on the complete demographics of individuals, which places constraints on the ability to ensure police accountability.
"The IPCA does not routinely report demographic variables such as age, ethnicity, and gender. The lack of systematic reporting of demographic information by the IPCA means that particular groups subject to armed police response cannot be specifically examined.
"Māori and Pacific people are more likely to be represented in crime statistics and there have been concerns of disproportionate police use of firearms against Māori.
"Māori are also more likely than non-Māori to experience mental distress and so to be involved in mental health-related police contacts. It is likely, therefore, that the sample analysed in this study also disproportionately included Māori experiencing mental distress being subject to the most extreme use of force by police."
They said the main value in their findings was to "bring the extent of police shootings that are mental health-related to the attention of all those involved in such events".
"Most individuals at the centre of mental health events were known to mental health services and/or the police. The very high proportion of cases where family/whanau were aware of the individual's mental health issues… suggests opportunities for police to use that information to engage with the individual… to minimise escalation of their response."
IPCA general manager Warren Young said the agency's previous database had impeded its ability to collate and reliably report on ethnicity.
However, a new system enabled it to record and report on the ethnicity of complainants "and others who are injured or killed as a result of police actions".
The IPCA intended to collate the information as part of its annual reporting.
"That does not mean that our individual public reports will include ethnicity data as a matter of course. The report states that the inclusion of ethnicity in public reports would provide 'public access to information on police practices in its entirety', but we do not get notified of, let alone publicly report on, every armed incident. It appears that the report is based on a misconception in this regard."
Police said the recognised the use of force was "a significant power granted" to them by consent of the public.
"So our use of force is always proportional to a person's threatening, violent and/or life-endangering behaviour,," said a spokesperson.
"Police use the least amount of force required to safely resolve the situation."
They said the events covered by this study were "often fast pace, complex, and extremely fluid".
"Requiring our staff to quickly consider a range of appropriate tactics to minimise harm to themselves and the wider community," said the spokesperson
"Our frontline staff undergo mental health training as recruits, and Police has refresher e-learning modules available for all staff."
Training to improve awareness of mental health was rolled out to all Police in 2016 including frontline staff.
"This training enables staff to recognise when people are in mental distress, respond appropriately and connect them to the relevant services available when able," the spokesperson explained.
"Research such as this is helps us improve our responses to those suffering from mental distress, and the training offered to first responders."
