The National Minimum Dataset (NMDS) is a national collection of public and private hospital discharge information, including coded clinical data for inpatients and day patients.
The NMDS is used by the Ministry of Health, DHBs, PHOs, clinicians, researchers and members of the public for statistical information, clinical benchmarking, and planning and funding.
The NMDS is used for policy formation, performance monitoring, research and review. It provides statistical information, reports, and analyses about the trends in the delivery of hospital inpatient and day-patient health services both nationally and on a provider basis. It is also used for funding purposes.
The NMDS is a national collection of public and private hospital discharge information, including clinical information, for inpatients and day patients. Unit record data is collected and stored. All records must have a valid NHI number.
Data has been submitted electronically in an agreed format by public hospitals since 1993.
The private hospital discharge information for publicly funded events, eg, birth events and geriatric care, has been collected since 1997. Other data is being added as it becomes available electronically.
The current NMDS was introduced in 1999. The original NMDS was implemented in 1993 and back-loaded with public hospital discharge information from 1988.
Guide for use
The NMDS has undergone many changes over the years. Some data subsets have been removed and are now held in separate collections (the Cancer Register and the Mortality Collection). In other cases, additional fields have been included and events are reported in more detail than in the past. For further details refer to the National Minimum Dataset (Hospital Events) (NMDS) Data Dictionary.
Private hospital information is also stored in the NMDS. Publicly funded events (primarily maternity and geriatric) and surgical events from some hospitals are up to date. Privately funded events may be delayed.
Collection methods – guide for providers
Data is provided by public and the larger private hospitals in an agreed electronic file format. Paper forms and a cut-down electronic file format are also forwarded by other private hospitals.
Frequency of updates
Publicly funded hospital events are required to be loaded into the NMDS within 21 days after the month of discharge. Electronic files are received and processed almost every day.
National Collections and Reporting has a team of staff who manually process private hospital electronic and paper reports.
Security of data
The NMDS is accessed by authorised National Collections and Reporting staff for maintenance, data quality, audit and analytical purposes.
Authorised members of the Ministry of Health and DHBs have access to the NMDS for analytical purposes, via the Business Objects reporting tool and the secure Health Information Network. Business Objects contains a subset of the data described in the Data Dictionary.
The Ministry of Health is required to ensure that the release of information recognises any legislation related to the privacy of health information, in particular the Official Information Act 1982, the Privacy Act 2020 and the Health Information Privacy Code 2020.
Information available to the general public is of a statistical and non-identifiable nature. Researchers requiring identifiable data will usually need approval from an approved Ethics Committee.
National reports and publications
The National Collections and Reporting Group publishes an annual report Selected Morbidity Data for Publicly Funded Hospitals. This publication contains summary NMDS information for a financial year.
This annual publication is available on the Hospital events page.
Customised datasets or summary reports are available on request, either electronically or on paper. Staff from the Analytical Services team can help to define the specifications for a request and are familiar with the strengths and weaknesses of the data. New fields have been added to the collection since 1988, but wherever possible consistent time series data will be provided.
The Analytical Services team also offer a peer review service to ensure that data from the national collections is reported appropriately when published by other organisations.
There may be charges associated with data extracts.