Who is excluded from official figures?
There are different groups of patients that are excluded from the official figures.
Pre-admit are the patients that have been given an appointment for their inpatient or day case treatment, generally within the next six weeks.
As of December 30, 2016 there were 22,927 patients who had been scheduled for treatment.
The other category of patients not officially counted is 'planned procedure' patients.
These are patients who have had initial treatment but who for clinical reasons require further action. These patients are in-treatment and have been provided with an indicative date or approximate time frame for the next stage.
This future treatment comes under the 'planned procedures' category. The NTPF said the majority of the 62,066 patients classified as planned procedures were for gastrointestinal endoscopies (48,774).
They have had an initial endoscopy but need to return for follow-on check-ups or further scopes at regular periods in the future to monitor their case.
It said that the same patients may be scheduled for multiple appointments in future years.
The NTPF, which compiles the figures, said it was currently commissioning a research project.
It is examining updated international best practice around publication models and methodologies and will review the outcome in due course.
Health Minister Simon Harris said he looked forward to the work being concluded and would take any action arising from its recommendations.