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Data Collection Overview

National Hospital Morbidity Database (NHMD)

Data Collection Sources

The National Hospital Morbidity Database (NHMD) is a compilation of episode-level records from admitted patient morbidity data collection systems in Australian hospitals. It is a comprehensive dataset that has records for all episodes of admitted patient care from essentially all public and private hospitals in Australia.
The data supplied are based on the National Minimum Data Set (NMDS) for Admitted patient care and include demographic, administrative and length of stay data, as well as data on the diagnoses of the patients, the procedures they underwent in hospital and external causes of injury and poisoning.
In 2011–12, diagnoses and external causes of injury and poisoning were recorded using the seventh edition of the International statistical classification of diseases and related health problems, 10th revision, Australian Modification (ICD-10-AM). Procedures were recorded using the seventh edition of the Australian Classification of Health Interventions (ACHI).

Institutional environments

The Australian Institute of Health and Welfare (AIHW) is a major national agency set up by the Australian Government under the Australian Institute of Health and Welfare Act 1987 to provide reliable, regular and relevant information and statistics on Australia’s health and welfare. It is an independent statutory authority established in 1987, governed by a management board, and accountable to the Australian Parliament through the Health and Ageing portfolio.
The AIHW aims to improve the health and wellbeing of Australians through better health and welfare information and statistics. It collects and reports information on a wide range of topics and issues, ranging from health and welfare expenditure, hospitals, disease and injury, and mental health, to ageing, homelessness, disability and child protection.
The Institute also plays a role in developing and maintaining national metadata standards. This work contributes to improving the quality and consistency of national health and welfare statistics. The Institute works closely with governments and non-government organisations to achieve greater adherence to these standards in administrative data collections to promote national consistency and comparability of data and reporting.
One of the main functions of the AIHW is to work with the states and territories to improve the quality of administrative data and, where possible, to compile national datasets based on data from each jurisdiction, to analyse these datasets and disseminate information and statistics.
The Australian Institute of Health and Welfare Act 1987, in conjunction with compliance to the Privacy Act 1988, (Commonwealth) ensures that the data collections managed by the AIHW are kept securely and under the strictest conditions with respect to privacy and confidentiality.
For further information see the AIHW website. Data for the NHMD was supplied to the AIHW by state and territory health authorities under the terms of the National Health Information Agreement.  
The state and territory health authorities received these data from public and private hospitals as stated below. States and territories use these data for service planning, monitoring and internal and public reporting. Hospitals may be required to provide data to states and territories through a variety of administrative arrangements, contractual requirements or legislation.

Relevance and Scope

The purpose of the NHMD is to collect information about care provided to admitted patients in Australian hospitals. The scope of the NHMD is episodes of care for admitted patients in all public and private acute and psychiatric hospitals, free standing day hospital facilities and alcohol and drug treatment centres in Australia. Hospitals operated by the Australian Defence Force, corrections authorities and in Australia's off-shore territories are not in scope, but some are included.
The counting unit in the NHMD is the separation. Separation is the term used to refer to the episode of admitted patient care, which can be a total hospital stay (from admission to discharge, transfer or death) or a portion of a hospital stay beginning or ending in a change of type of care (for example from acute care to rehabilitation).
The hospital separations data do not include episodes of non-admitted patient care provided in outpatient clinics or emergency departments. Patients in these settings may be admitted subsequently, with the care provided to them as admitted patients being included in the NHMD.
The NHMD is the source of information for 3 performance indicators for the National Healthcare Agreement and other national performance reporting.
Although the NHMD is a valuable source of information on admitted patient care, the data have limitations. For example, variations in admission practices and policies lead to variation among providers in the number of admissions for some conditions (such chemotherapy and endoscopies).
Relevant maternal and perinatal morbidity-related data items from the NHMD have been listed in the Maternity Information Matrix. The data items of Principal diagnosis, Additional diagnosis, External cause, Place of occurrence of external cause and Activity when injured contain ICD-10-AM codes that would be relevant to multiple categories of data items in the Matrix, including: Antenatal, Labour and Birth, Complications of Labour, Maternal Morbidity, Puerperium, Maternal Mortality, Fetal and Neonatal Morbidity and Fetal and Neonatal Mortality. These items have not been repeated in all of these sections of the Matrix but users should note their applicability to different sections when searching for information. Users will need to refer to the International statistical classification of disease and related health problems – Australian Modification (ICD-10-AM) for the appropriate maternal and perinatal codes.


The reference period for this data set is 2011–12. This includes records for admitted patient separations between 1 July 2011 and 30 June 2012. 
All states and territories had provided a final version of the data by 4 March 2013. The data were published on 19 April 2013.


States and territories are primarily responsible for the quality of the data they provide. However, the AIHW undertakes extensive validations on receipt of data. Data are checked for valid values, logical consistency and historical consistency. Where possible, data in individual data sets are checked with data from other data sets. Potential errors are queried with jurisdictions, and corrections and resubmissions may be made in response to these edit queries. The AIHW does not adjust data to account for possible data errors or missing or incorrect values, except as stated.
Although there are national standards for data on admitted patient care, statistics may be affected by variations in admission and reporting practices across states and territories. For example there are some variations in how hospital services are defined and counted, between public and private hospitals, among the states and territories, and over time.
For 2011–12, principal diagnosis information was not provided for approximately 3,000 public hospital separations and 1,000 private hospital separations.

There was variation between states and territories in the reporting of separations for Newborns (without qualified days). For 2011–12:
•     Private hospitals in Victoria did not report most Newborn episodes without qualified days; therefore the count of newborns will be underestimated.
•     South Australian private hospitals are not required to provide records for Newborn episodes without qualified days.
•     For Tasmania, where a newborn’s qualification status was considered qualified at any point during the episode of care, the entire episode was reported as qualified days. As a consequence, the average length of stay for Newborn episodes with qualified days only in Tasmanian public hospitals is not directly comparable with that in other jurisdictions.
•     The private hospital in the Northern Territory reported separations for Newborn episodes with qualified days that may not have involved qualified care.
While the Indigenous status data in the NHMD for all states and territories are considered of sufficient quality for statistical reporting for 2010–11 and 2011–12, separations for Aboriginal and Torres Strait Islander people are under-enumerated (see AIHW 2013 for more information). Caution should be used in the interpretation of Indigenous status data because of the under-enumeration overall and differences in under-enumeration among the jurisdictions. The quality of the data for private hospitals is not known, but likely to be poor.

Not all states provided information on the area of usual residence of the patient in the form of a Statistical Local Area (SLA) code for all presentations. In addition, not all states and territories provided the version of SLA specified in the NMDS.

Where necessary, the AIHW mapped the supplied area of residence data for each presentation to the same SLA and to remoteness area categories based on the ABS ASGC Remoteness Structure for 2006. This mapping was done on a probabilistic basis. Because of the probabilistic nature of the mapping, the SLA and remoteness areas data for individual records may not be accurate and reliable; however, the overall distribution of records by geographical area is considered useful.

Socioeconomic status is based on the reported area of usual residence of the patient. The SEIFA categories for socioeconomic status are assigned at the national level, not at the individual state/territory level.
More details can be found in the NHMD Data Quality Statement: 2011–12.


The AIHW provides a variety of products that draw upon the NHMD. These include the Australian hospital statistics suite of products with associated Excel tables which can be accessed on the AIHW website.


Metadata information for the National Minimum Data Sets that are the basis for the AIHW National Hospital Databases are published in the AIHW’s online metadata repository—METeOR, and the National health data dictionary.

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