The Ministry of Health's Hearing Aid Funding Scheme is being described as a post code lottery.

New research shows that 33 percent of DHBs aren't paying installation costs for Ministry of Health funded hearing aids.

National Foundation for the Deaf CEO Louise Carroll says dual disability or low income patients are missing out because of this.

"It's a bit of what we call a post code lottery as to where you're living in New Zealand as to whether you can get the hearing aid funding scheme up and running."

Carroll says the very people who need assistance are missing out.

"You can't have a hearing aid unless it's fitted properly by an audiologist because you don't know what your clinical needs are, so it's a ludicrous situation and we're asking for a review of this policy."