Estimated rates of mental disorders in, and situational characteristics of, incidents of nonfatal use of force by police

To examine the estimated rates of mental disorders and associated situational characteristics in people involved in nonfatal
use of force incidents with police in VIC, Australia.

A random sample of 4,267 cases between 1995 and 2008 from a dedicated police Use of Force Register were linked with the state-wide
public mental health database and a police contacts database. Rates of ICD 9 and ICD 10 mental disorders recorded on the public
mental health database were examined, as well as rates of criminal offending and the characteristics of force used by both
parties.

More than a third of people on whom the police resorted to using force (n = 1,621, 38 %) had a history of mental disorder. Significant overrepresentations of the estimated prevalence of psychosis
[12.5 %, OR = 9.03, 95 % CI (7.41, 11.01), p < 0.001] and schizophrenia [9.1 %, OR = 9.73, 95 % CI (7.59, 12.47) p < 0.001] were found. Those diagnosed with mental disorders were 1.52 times more likely to use or threaten to use weapons
on police, even after taking into account age, sex, substances intoxication and violent behaviour [95 % CI (1.23, 1.91), p < 0.001]; however, they were no more likely to injure or be injured by police than those without a recorded history of mental
disorder. There was a noted trend for police to use, or threaten to use, weapons on people with a history of psychosis (other
than schizophrenia) [OR = 1.40, 95 % CI (1.11, 1.78), p = 0.005].

Psychoses and schizophrenia are dramatically overrepresented in cases where police resort to using force. Situational characteristics
evident in the encounters are suggestive of a sub-group of people with mental disorders presenting with aggressive and otherwise
problematic behaviours coupled with histories of criminal offending; this presents significant ongoing challenges for the
police.