Nine out of ten New Zealand MPs have been victims of harassment, which has sometimes included physical violence, a new study shows.
The research paper by the University of Otago and Capital and Coast District Health Board is based on anonymous responses from 102 sitting MPs and finds 87 per cent of them have been targets of harassment, ranging from abusive emails to violence.
"The harassment of politicians in New Zealand is common and concerning," the paper's co-authors Suzanne Every-Palmer, Justin Barry-Walsh and Michele Pathe wrote.
Half of the MPs surveyed had been personally approached by their harassers, and 15 per cent had been physically attacked.
It said some of these incidents were serious and involved weapons such as guns, Molotov cocktails and blunt instruments.
The paper referred to MPs being sent death threats by text message, receiving email with pornographic images and references to their children, and getting 1080 poison in the mail.
In one case, an MP had their back door smashed in and a bullet thrown through their bathroom window.
Parliamentary Services keeps records of threatening behaviour, and identified 600 people as potential security risks at any one time.
While the research was being carried out, a man equipped with a firearm arrived on the Parliamentary precinct, forcing Parliament into a lockdown.
The authors of the paper said the "small, but significantly elevated risk" of violence towards politicians was not the result of organised terrorism or politically motivated extremists but came from fixated individuals with untreated, serious mental health disorders.
The study cited the case of Australian "lone wolf" Man Haron Monis, who held 18 people hostage in the Lindt Café in Sydney last year before killing himself and two others.
Monis had a record of harassing public figures.
Russell John Tully, who is charged with killing three Work and Income staff in Ashburton last year, had also signalled his growing frustrations with politicians before the attack.
The paper stressed that the vast majority of people with mental illness did not harass or stalk public figures and out of the small fraction that do, only a minority behaved violently.
"However, despite the small numbers, untreated mentally disordered fixated individuals can cause significant societal harm."
They said the threats to MPs should be more closely monitored because politicians were often targeted by severely ill people who could pose a threat to the wider public.
"The results provide support for the creation of a specialised threat assessment service. This would hopefully benefit Parliamentarians, their families, staff and the public, and facilitate access to psychiatric treatment for the mentally disordered fixated individual."
In July, Mana leader Hone Harawira found bullet holes in his electorate office's front window in Kaitaia.
He said at the time: "It is a worry, I get criticisms, I get threats - I even get death threats - but when people start taking shots at your office it's a whole different ball game."
In August 2012, a man who had been badly affected by the Christchurch earthquakes was charged with threatening to kill Earthquake Recovery Minister Gerry Brownlee.
Former Green Party co-leader Sue Bradford also received death threats during the debate on her anti-smacking bill.
The research paper, which was published in the Australian and New Zealand Journal of Psychiatry, said politicians felt they and their families were more exposed as a result of the internet, and they reported that cyberstalking and online harassment was common.