Asylum-seekers detained offshore by Australia have a 20 times greater risk of post-traumatic stress disorder compared with those detained on the mainland for less than six months, researchers have found.
In a letter to the editor published on Tuesday in the British Journal of Psychiatry, University of New South Wales researchers detailed their survey of nearly 1000 adult refugees and asylum seekers living in the Australian community between 2011 and 2018.
More than 20 per cent of the cohort had experienced some form of immigration detention before eventually joining the Australian community.
It's the first of its kind empirical research looking at the long-term psychological impact of offshore processing by comparing them to people held in immigration detention centres on the mainland.
Successive Australian governments since 2013 have held asylum-seekers in Nauru and on Manus Island in Papua New Guinea, before it was shut down by court order in 2017.
"This survey data allowed us to test for the first time whether previous experiences of offshore detention impacted someone's risk of experiencing long-term serious mental illness once living in the community, by comparing them to people who had been detained onshore for less than six months," lead researcher and clinical psychologist Philippa Specker said.
"We found that if you had been in onshore detention for longer than six months, or offshore detention for any length of time, your risk of having subsequent PTSD, depression or suicidal ideation was significantly greater, and of a magnitude that really surprised us."
The psychologists found even worse mental health outcomes among those who spent a longer period in onshore detention, compared to those who were released within six months.
The average length of time people were detained in an Australian centre was 545 days or 1.5 years.
Last year, the High Court ruled in a landmark decision that non-citizens could not be kept in indefinite immigration detention, which led to the release of some 215 detainees with restrictive conditions such as ankle monitors and curfews.
The study comes days after the Albanese government passed new regulations following another High Court decision that deemed the restrictions placed last year were punitive and unconstitutional.
The new raft of measures, which legal experts and human rights advocates have labelled short-sighted and cruel, allows Australia to pay third countries for their resettlement.
Home Affairs Minister Tony Burke told parliament on Thursday "that is why we introduced powers today to improve the government's capacity to remove people from this country in this situation".
But Dr Specker maintains practical rather than punitive measures can be used to resolve the problem of displaced people seeking safety.
"We understand that when someone's arriving to a new country and they're seeking asylum and lodging an asylum claim, of course, that requires some degree of administrative processing."
"What our findings are telling us is that the way a person is treated while their asylum claim is being processed can make a really big difference."
She pointed to how UNSW's Kaldor Centre for International Refugee Law calculated that holding someone in offshore detention is 5550 times more expensive for taxpayers than allowing them to live in the Australian community while their claim is processed.
"It is not too late for Australia, and other governments seeking to establish similar models of offshore processing and immigration detention, to instead consider evidence-based alternatives."
