The last time Rudey* went to jail, for three weeks, she didn't speak to anyone outside. She wanted to let people know where she was, to get someone to feed her cat and check on her flat, but the prison's phone system defeated her; she couldn't figure it out and didn't want to draw attention to herself by asking for too much help.

Now 47, Rudey acquired a brain injury about four years ago after being assaulted. She can't work or study and now has a live-in carer, Jeff, who says matter-of-factly that it's a lot like living with a teenager. "She leaves the stove on, forgets a lot."

Rudey is not sure whether anyone in the prisons system knew she had an acquired brain injury (ABI). She doesn't remember anyone asking and says there was no special help or support, despite her obvious difficulty explaining herself and managing some everyday tasks.

Over those three weeks she showered about three times – a broken finger made things awkward and the shower curtain didn't seem to work so there was little privacy. She also ate very little and was grieving for her mother and an uncle, both of whom had recently died.

"I was just so sad and I was in pain. It was all so frustrating."

Having access to what she calls a third person, someone to help explain things to her and help her express herself, would have made a huge difference. "If there had been a third person at the police station I don't think I would even have gone to jail. I was so overwhelmed, it was like I was speaking another language."

People with disabilities, such as acquired brain injury, are vastly over-represented in prisons, but until now there has been little data about the extent or type of disability.

Disability in prisons is invisible and mostly ignored

For the first time, researchers are compiling figures on the number of disabled prisoners. This group is largely invisible in official records and experts argue that with little support inside, they are less able to cope with jail and are virtually guaranteed to end up back inside, effectively a double punishment.

Previous research found about 42 per cent of male prisoners had an acquired brain injury, compared with about 2 per cent in the general population. Another study found that more than 40 per cent of Victorian prisoners had a psychiatric risk rating, indicating that they had a mental health issue.

New research has also found that young Indigenous people with foetal alcohol spectrum are greatly over-represented in prisons.

Professor Stuart Kinner, of Griffith University's Criminology Institute and its Menzies Health Institute, said in 2015 for the first time the standard disability flag was added to national data collected every three years on the health of people moving through the prisons system. The measure of disability is based on a World Health Organisation definition and assesses the functional impact of having a disability, such as difficulty participating in education and work.

Early data using the standard disability flag has found 30 per cent of prisoners have long-term health conditions or disability that restrict their ability to participate in employment and education and limit their general activities.

Almost two-fifths (38 per cent) of prisoners aged 35-54 had limited activity or participation in work or education, compared with 14 per cent of the general population.

Kinner said there was little evidence of programs for disabled prisoners and because prisons are state-based there was no requirement for co-ordination.

"We are not picking up people who have significant needs in the prisons system. This has major implications for their ability to follow instructions, take medication … for their day-to-day functioning. Making sure we identify those people is critical to their appropriate management in prison."

He said people with mild to moderate disability are particularly over-represented in prisons. "These may be people who are falling through the cracks, and this has contributed to them ending up in prison in the first place."

Kinner said such disabilities often involved complex health needs that were not being met in the corrections system.

"There's a large number of people who experience significant functional impairment, with a range of health problems and learning challenges. They may have a life-time's experience at how to cover these up. There's a strong incentive to cover up some disability in prisons, it can make you quite vulnerable."

The 2015 Ombudsman's report found that Prisons Victoria was not routinely screening people who come into prisons for disability, including cognitive and psychiatric disabilities. The Ombudsman also found that many prisoners were not getting special help for their disability.

The report highlighted the example of a special unit for people with intellectual disability at the Port Phillip Prisons, Marborough Wing. While the specialist wing has 35 beds the Ombudsman found there were 95 people registered in that prison with an intellectual disability.

Disabled prisoners vulnerable

Michelle McDonnell, spokesperson for the Smart Justice Project, led by the federation of community legal centres, said prisoners with an intellectual disability were particularly vulnerable to bullying and harassment and when their condition had not been formally diagnosed their behaviour was often seen by staff as disobedience and they may be punished.

McDonnell said there was also evidence that people with disabilities spent longer in prison because they were less able to access parole because of barriers such as difficulty getting secure accommodation and problems negotiating the justice system.

"We've had a 68 per cent increase in the prison population [over 10 years to 2014], that's why all the money has gone on infrastructure and not on services. If we really want to reduce the reoffending rate it makes sense to support people with disability both inside and outside prison."

Researchers at Melbourne University's School of Population and Global Health, who screened people for intellectual disability after their release from jail, found that those with this impairment were significantly less able to manage their own health care after their time in jail.

Rudey is taking part in a project jointly run by Jesuit Social Services and RMIT's Centre for Innovative Justice, which aims to support ex-prisoners with an ABI and provide recommendations about how the criminal justice system can improve its awareness of this disability. The researchers have been working with a group of ex-prisoners with ABI for the past year.

Anna Howard, coordinator of the Enabling Justice Project said that for most of those who had participated in the project the prison system had been unaware of their ABI and they had received no extra support while in jail.

Howard said access to housing, support in the early stages of their involvement with the criminal justice system and help transitioning out of prison were crucial. The Assessment and Referral Court, for people with mental health issues or cognitive impairment, includes a case worker for each person charged with a crime, and was very successful but was run out of the Melbourne Magistrates Court and not available at any other court.

"The specialist services available for people with ABI in prisons are very, very limited, only the most severe cases ever get them. When you're talking about almost half of the prison population, the question isn't only whether the prison can respond appropriately, it is why so many people with a disability are in there and whether there is a smarter way to respond to disability. In our view, there needs to be a system-wide change in the approach to disability".

*Name has been changed.