Less than a third of sexual violence cases reported to police are making it to court and only about a tenth are ending in convictions, according to official figures.
Just 6 per cent are leading to imprisonment.
In the first large-scale research of its kind in New Zealand, the Government has released an analysis of 23,739 cases of reported sexual violence victimisations from 2014 to 2018.
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The report, commissioned by Under-Secretary for Justice Jan Logie, aims to lay out the statistics behind the struggles of victims to get their cases through the legal process.
"For too long, too many people have faced barriers accessing our justice system," Logie said.
"This isn't good enough … No single agency or department can fix this on their own. We have to work together, work differently and work across the whole justice system so every person harmed can get the resolution they need."
She said it was shocking that it had taken until 2019 for a Government to put the data together.
Key findings of the study include:
• For every 100 cases of sexual violence reported to police, only 31 result in court action, 11 end in convictions and 6 in a jail sentences
• The number of reported increased by 21 per cent from 2014-15 to 2017-18.
• There had been a 34 per cent increase in the number of investigations leading to court action in the most recent year.
The report concluded most cases had dropped off during the initial stage of the process, with police only taking action against perpetrators in 37 per cent of cases between 2014 and 2018.
It also found because of changes to police practices, the number of victimisations being not classed as crimes by officers had fallen from 17 per cent of reported cases in 2014 to 2 per cent in the past year.
Logie said that figure was a "slither of good news".
"But there is still a very long way to go. This Government is committed to making progress on these long-term challenges," Logie said.
"We are going to be relentless in turning this around. Because people deserve better."
A Herald investigation this year found historical data on sex crimes had been deeply misleading, with police labelling reports of cases with limited evidence or intoxicated victims as "no crime disclosed". There had been a sharp rise in reported cases since police reviewed the practice in 2014.
A report for the Ministry of Justice this year looking at the experiences of victims found that the system revictimised and retraumatised complainants, particularly during the trial process.
The Government in July announced it planned to change the rules for how sexual violence complainants gave evidence for trials, in a bid to reduce trauma from the process and improve reporting rates.
The legislation is expected to be introduced later this year.
The proposals include tightening rules around questioning of victims about their sexual histories, and allowing recording of evidence by complainants for use at re-trials.
Some lawyers, however, have raised concerns that they could impact fair trial rights and hinder defences.
This year's Budget included about $38 million for the reforms.
Trials of specialised sexual violence courts in Auckland and Whangarei were also made permanent this year after a report found they reduced wait times and anxiety for victims.
The pilots were established in 2016 and saw judges given special training in handling the cases, with a greater focus on pre-trial management.
Justice Minister Andrew Little in August said while an expansion to other districts made sense, no resources had been allocated to expanding the scheme and a nationwide rollout was likely take several years.
Where to get help
To contact police, call 111
Rape Crisis NZ: 0800 883300 or for a local branch detail, visit http://www.rapecrisisnz.org.nz/