The Health Minister Simon Harris says there are still too many people who have to wait for treatment.

Minister Harris was responding to data which shows the number of patients waiting for operations or medical procedures is considerably higher than the numbers on the waiting lists published by the the National Treatment Purchase Fund (NTPF).

The NTPF has responsibility for collating waiting list data.

However, the minister says as of last December only 2% of patients were waiting longer than 18 months for treatment.

In a statement, Minister Harris said: "Last summer I requested that the HSE (Health Service Executive) put in place an action plan to halve the number of patients waiting over 18 months for treatment.

"Last month, I announced the successful completion of this action plan with over 11,500 patients coming off the inpatient/daycase waiting list in the second half of 2016.

"However, I think it is important to note that, while there are still too many people who have to wait too long for their treatment, as of last December, only 2% of patients were waiting longer than 18 months for treatment.

The minister says 93% were receiving treatment within 15 months - and over half were receiving treatment within six months.

He has also asked the HSE to submit an action plan to improve waiting lists in the public acute hospital sector for inpatients, daycases and outpatients.

He expects to receive this "shortly".

He said the HSE and the NTPF will work "strategically and collaboratively together" to ensure the best use of public and private hospital capacity to reduce patients waiting times.

In relation to concerns raised about the NTPF figures, he added: "I understand the waiting list figures have been consistently counted the same way since the establishment of the NTPF and follow other international models, for example Sweden and Canada.

"The NTPF waiting list figures provide an up-to-date and verified picture of patients actively waiting for a date for treatment.

"The approach here is in line with international protocols but it is important the NTPF keeps its processes under regular review to ensure best practice and it is welcome the fund is currently commissioning a research project examining updated international best practice around publication models and methodologies."

Over 81,000 on inpatient waiting list

The discrepancies in the data were uncovered by an RTÉ Investigates piece, which aired on Monday.

The programme followed patients who spend months, and even years, waiting to get an appointment to see a doctor or have a procedure.

The total number of people waiting on the inpatient/daycase waiting list as published by the NTPF on the December 30th last year was 81,015.

However evidence was uncovered that shows there are at least two other waiting lists which are not published by the NTPF.

One of those is the pre-planned list containing names of thousands of patients who require follow up treatment.

Patients on the pre-planned list are typically given indicative dates for their procedures. These dates can range from less than six weeks to more than 12 months.

The breakdown of the figures on the list indicate many of the indicative dates are not delivered on by the hospitals.

The second list is known as the pre-admit list. It too contains thousands of patients from across the country waiting up to 18 months on surgical procedures.

In a statement the NTPF said: "In line with international best practices, published waiting list data excludes patients classified as pre-admit and pre-planned procedures"

It also said the NTPF is currently "examining updated international best practice around publication models".