It has never been tougher to make a successful claim for the Disability Support Pension (DSP), new Government figures suggest.

Key points: Vast majority of DSP applicants being rejected

Vast majority of DSP applicants being rejected Advocates say successful claims "plummeted" over past year

Advocates say successful claims "plummeted" over past year Government says rule changes fair and reasonable

Hundreds of thousands of people who are unable to work more than 15 hours a week rely on the payment.

But statistics from the Department of Social Services obtained by the ABC indicate only about 15 per cent of current applicants are granted the DSP.

The vast majority are rejected.

That is more than a 50 per cent drop in the so-called "grant rate". In 2014-15, more than a third of claimants were granted the DSP.

On July 1, 2015, new rules for claiming the DSP came into effect. A two-stage process was introduced.

Claimants undergo a Job Capacity Assessment.

If it is concluded they meet the DSP criteria, they move on to what is known as the Disability Medical Assessment.

An email from the Department of Social Services states the Department of Human Services (Centrelink) finalised 51,691 DSP claims, which were lodged between July 1, 2015 and March 31, 2016.

Of those claims, it said 5,199 (about 10 per cent) included a Disability Medical Assessment. Most DSP claims require a medical assessment before they are granted.

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Historically, about 5 per cent of claimants were granted the DSP without a medical assessment because their disability was already clear — something the Government calls "manifest" cases.

Those figures, taken together, suggest a current grant rate of about 15 per cent.

"To see it plummet in a year actually raises a question about whether the changes have undermined the reliability of the process," Matthew Butt, from the National Welfare Rights Network. said.

"A lot of people might get lost in the system. It's always the most vulnerable people who are most likely to challenge a Centrelink decision."

Applicant left waiting for months to hear about claim outcome

Dale Sheppard said it had been impossible to get answers about his application. ( Supplied )

For many people now in the process of applying for the DSP, revelations of the low grant rate are not a surprise. There are many stories of delays stretching longer and longer.

"I submitted (my application) in November. And to get an answer about whether I'm successful, eligible, or any of those, it's almost impossible," said Dale Sheppard, a 38-year-old quadriplegic who lives near Melbourne.

After years of running his own business, he found he was growing too fatigued to work a full week. He decided to apply for the DSP.

He said it had not been easy.

He shared a screen shot of his phone, which showed it recently took 37 calls to reach Centrelink's automated phone system, and another hour on hold to speak with an operator.

"You just go, 'this is not getting anywhere', and then you just go, 'I'm stuck'," he said.

"I just have to wait."

Mr Sheppard is still waiting to hear from Centrelink whether he will be granted the DSP, or if he will be rejected.

It took Dale Sheppard 37 calls to get through to Centrelink. ( Supplied )

The Department of Social Services did not respond directly when asked to comment on the 15 per cent grant rate figure.

The Department of Human Services said the grant rate at December 2015 was 22 per cent — based on publicly available data.

A spokesman for Social Services Minister Christian Porter defended the rule changes — particularly the medical assessments now being performed by doctors contracted by the Government.

"This fair and reasonable measure will have an impact over time on the growth in numbers of new DSP applicants and entries to the system," the statement said.

"This move is nothing more than good administrative common sense."

But many of those in the process are especially frustrated by delays between the stage one Job Capacity Assessment and the stage two Disability Medical Assessment.

"I think the hardest thing was the wait," said Deb Schwerdt, who spent nearly six months directing the DSP application for her 19-year-old son, Jacob, who has autism.

Jacob was eventually granted the DSP, but not before the family worried about what he would do after finishing school. As a DSP recipient, he is eligible for special employment assistance that can help him transition to a part-time job.

"There was no feedback that it was going to take longer, how long it would take. So often you felt like, 'is this happening?'"