Classifications and technical notes

Health‑related classifications have multiple purposes, including the facilitation of data collection and management in the clinical setting, the analysis of data to inform health policy, and the allocation of financial and other resources. This section provides a short description of the classification systems referenced in this report.

Australian Classification of Health Interventions

The Australian Classification of Health Interventions (ACHI) is the Australian national standard for procedure and intervention coding in Australian hospitals.

The National Centre for Classification in Health (NCCH) developed the ACHI based on the Medicare Benefits Schedule (MBS). The MBS is a fee schedule for Medicare services including general practice consultations, specialist consultations, surgical procedures and other medical services, such as diagnostic investigations and optometric services. The Australian Government Department of Health, Disability and Ageing updates the MBS at least twice each year and these code changes are incorporated into the ACHI or the MBS items are mapped to existing ACHI codes.

The ACHI classifies procedures and interventions performed in public and private Australian hospitals, day centres and ambulatory settings, as well as allied health interventions, dentistry and imaging. The structure of the ACHI is anatomically based, rather than based on the medical specialty.

To maintain parity with disease classification, ACHI chapters resemble the International Statistical Classification of Diseases and Related Health Problems, 10th revision, Australian Modification (ICD-10-AM chapters). The ACHI is updated biennially by the National Casemix and Classification Centre (NCCC) in line with the disease section of the ICD-10-AM. Use of codes is guided by the Australian Coding Standards of the ICD-10-AM.

Further information on the ACHI is available from the Independent Health and Aged Care Pricing Authority (IHACPA) website.

Primary Health Networks

Primary Health Networks are organisations that connect health services across a specific geographic area (a PHN area), with the boundaries defined by the Australian Government Department of Health, Disability and Ageing. There are 31 PHN areas that cover the whole of Australia. Further information is available on the Department of Health, Disability and Ageing website.

Australian Statistical Geography Standard

The Australian Statistical Geography Standard (ASGS) was developed by the ABS for the collection and dissemination of geographically classified statistics. It is a common framework that enables publication of statistics that are comparable and spatially integrated and is an essential reference for understanding and interpreting the geographical context of Australian statistics.

The ASGS is updated every 5 years to account for growth and change in Australia’s population, economy and infrastructure. For the 2021 release, the ASGS was updated to the Australian Statistical Geography Standard (ASGS) Edition 3 (ABS 2021). ASGS Edition 3 was used for the 2021 Census of Population and Housing, and was introduced into some data collections from 2022–23. ASGS Edition 3 is an update of ASGS Edition 2 (2016).

Please refer to details in the ASGS Edition 3 on the ABS website.

Statistical Areas

Statistical Areas are a geographical classification defined by the ABS and included in the ASGS. They encompass 4 levels, with increasing size and population: Statistical Areas Level 1 (SA1); Statistical Areas Level 2 (SA2); Statistical Areas Level 3 (SA3); and Statistical Areas Level 4 (SA4).

In some data sections, where applicable, data from previous collection periods where data were reported with SA2 and SA3 2011 boundaries were mapped to 2016 boundaries for data between 2017–18 and 2021–22 (inclusive) and mapped to 2021 boundaries for data since 2022–23 to allow for historical comparisons. Correspondence are sourced from the ABS.

Remoteness

In this report, the ASGS applies to the data presented by remoteness area. For data from 2017–18 to 2021–22 (inclusive), the ASGS Edition 2 (2016) is used; earlier years use ASGS Edition 1 (2011); and from 2022–23 onwards, the ASGS Edition 3 (2021) is used. ASGS is categorised into Remoteness Areas (RAs). RAs aggregate to states and territories and cover the whole of Australia without gaps or overlaps (ABS 2016b).

This report uses the ASGS to present data in the following categories:

• Major cities
• Inner regional
• Outer regional
• Remote
• Very remote.

For further information on this classification system, refer to the ABS website.

Socio-economic status

The ABS Socio Economic Indexes For Areas Index of Relative Socio-economic Disadvantage (SEIFA IRSD) is used to report Australian socio-economic data (ABS 2013, 2016c, 2021b). SEIFA scores are calculated by taking into account a range of information about economic and social conditions, such as education, occupation, employment, income, families, and housing of people and households within an area. The index is used to summarise the socioeconomic conditions of a geographical area (ABS 2013, 2016c, 2021b). IRSD only includes measures of relative disadvantage.

These scores are categorised into 5 groups, referred to as quintiles, which each represent one-fifth (20%) of the Australia areas (ABS 2013, 2016c, 2021). Quintile 1 is the most disadvantaged group and quintile 5 is the least disadvantaged group (ABS 2013, 2016c, 2021b). A geographical area with a low SEIFA score will likely comprise of a higher proportion of people who are relatively disadvantaged and a lower proportion of people who are relatively advantaged.

More information can be found on the ABS website.

Anatomical Therapeutic Chemical Classification System

The Anatomical Therapeutic Chemical (ATC) Classification System, developed by the World Health Organization (WHO), assigns therapeutic drugs to different groups according to the body organ or system on which they act, as well as their therapeutic and chemical characteristics (WHO 2011).

The coding of pharmaceutical products within the Pharmaceutical Benefits Scheme is based on the ATC Classification System but with some differences as outlined in the relevant data source sections.

For further information on this classification system, refer to the WHO website.

International Classification of Diseases

The International Classification of Diseases (ICD), which was developed by the WHO, is the international standard for coding morbidity and mortality statistics. It was designed to promote international comparability in the collection, processing, classification and presentation of these statistics. The ICD is periodically reviewed to reflect changes in clinical and research settings (WHO 2010).

Although the ICD is primarily designed for the classification of diseases and injuries with a formal diagnosis, it also classifies a wide variety of signs, symptoms, abnormal findings, complaints and social circumstances that may stand in place of a diagnosis.

Further information on the ICD is available from the WHO website.

International Statistical Classification of Diseases and Related Health Problems, 9th revision, Clinical Modification

The International Statistical Classification of Diseases and Related Health Problems, 9th revision, Clinical Modification (ICD–9–CM) is based on the ninth revision of the ICD (NCC 1996). The ICD–9–CM was the official system of assigning codes to diagnoses and procedures associated with hospital use in Australia before it was superseded by the ICD–10–AM.

International Statistical Classification of Diseases and Related Health Problems, 10th revision, Australian Modification

The Australian Modification of ICD–10 (called ICD–10–AM) is widely used to classify diagnoses in the health sector in Australia. It is used in public and private hospitals, and in community and residential mental health care services. The ICD–10–AM was developed in Australia by the NCCH with the purpose of making ICD–10 more relevant to Australian clinical practice (NCCH 2006).

References

ABS (Australian Bureau of Statistics) 2011. Australian Statistical Geography Standard (ASGS): Volume 5 – Remoteness Structure, July 2011. ABS cat. No. 1270.0.55.005. Canberra: ABS.

ABS (2013). Socio-Economic Indexes for Areas (SEIFA). ABS. accessed 17 February 2026

ABS (2016). Australian Statistical Geography Standard (ASGS): Volume 1 – Main Structure and Greater Capital City Statistical Areas, July 2016. ABS cat. No. 1270.0.55.001. Canberra: ABS.

ABS (2016b). Australian Statistical Geography Standard (ASGS): Volume 5 – Remoteness Structure, July 2016. ABS cat. No. 1270.0.55.005. Canberra: ABS.

ABS (2016c). Census of Population and Housing: Socio-Economic Indexes for Areas (SEIFA), Australia, 2016. ABS cat. No. 2033.0.55.001. Canberra: ABS.

ABS (2021). Australian Statistical Geography Standard (ASGS) Edition 3. ABS, accessed 17 February 2026

ABS (2021b). Socio-Economic Indexes for Areas (SEIFA), Australia. ABS, accessed 17 February 2026

NCC (National Coding Centre) (1996). The Australian version of the international statistical classification of diseases and related health problems, 9th revision, clinical modification. Sydney: NCC.

NCCH (National Centre for Classification in Health) (2006). The international statistical classification of diseases and related health problems, 10th revision, Australian modification. Sydney: NCCH.

WHO (World Health Organization) (2010) International classification of diseases (ICD), World Health Organization, accessed 17 February 2026.

WHO (2011) Anatomical Therapeutic Chemical (ATC) Classification, World Health Organization, accessed 17 February 2026.

This section provides a list of codes used to define mental health-related hospital separations from the National Hospital Morbidity Database (as used in the Admitted patients section).

National Hospital Morbidity Database data

Data from the National Hospital Morbidity Database (NHMD) are the source for the Admitted patients section of this online report. The definition of the scope of each section is provided in the section’s introduction or data source. Key elements of these definitions depend on the ICD-10-AM diagnosis codes and the Australian Classification of Health Interventions (ACHI) procedure codes. The codes in-scope are listed below.

During the preparation of Mental health services in Australia 1999–00 (AIHW 2002), attention was given to ensuring that, for data on hospital separations from the NHMD, the definition of a ‘mental health-related diagnosis’ included all codes that were either clinically or statistically relevant to mental health. This definition was revised for Mental health services in Australia 2000–01 (AIHW 2003) to increase the accuracy of the data. More specifically, for the analyses of the 2000–01 National Hospital Morbidity data, a diagnosis was considered clinically relevant to mental health if:

• it was included as a principal diagnosis defining Australian Refined Diagnosis Related Group Version 4.2 Major Diagnostic Categories (MDC) 19 (Mental diseases and disorders) and 20 (Alcohol/drug use and alcohol/drug induced organic mental disorders) or
• it appeared to be specific for a mental health-related condition based on expert advice.

A diagnosis was defined as being statistically relevant to mental health if:

• during 2000–01 there were more than 20 separations with specialised psychiatric care for that principal diagnosis at the 3-character level of ICD-10-AM or more than 10 at the 4-character level or
• over 50% of separations with that principal diagnosis included specialised psychiatric care.

This method was developed in consultation with the former Mental Health Information Strategy Standing Committee and the Clinical Casemix Committee of Australia.

Certain codes were statistically relevant during 1999–00 but not in 2000–01; these were examined and included if over 50% of total separations over the 2 years included specialised psychiatric care.

For the Mental health online report, the same codes used for the analysis of the 2000–01 data have been used to define ‘mental health-related’ hospital separations in the Admitted patients section. However, updates have been made to incorporate changes in codes that have occurred as new editions of ICD-10-AM have been released.

The full list of codes used to define mental health-related hospital separations is shown in the following table.

.. not applicable
Y code used

1. Excluding F00.00, F00.10, F00.20, and F00.90
2. Excluding F01.00, F01.10, F01.20, F01.30, F01.80, and F01.90
3. Excluding F02.00, F02.10, F02,20, F02.30, F02.40, and F02.80
4. Excluding F03.00
5. Excluding F52.5
6. Excluding F84.2 (ICD-10-AM 11^th Edition), F85 (ICD-10-AM 12^th Edition).2
7. Excluding F98.5 and F98.6
8. Excluding 099.32

Procedures component of the definition of ambulatory-equivalent mental health-related separations

The reporting of ambulatory-equivalent mental health-related separations as a separate category ceased in 2017–18 and this section is retained for historical reference only.

The full list of ACHI codes as part of the definition of ambulatory-equivalent mental health-related hospital separations is shown in the following table. If there is no procedure recorded, or only procedure(s) in this list, and the following criteria are met, then the separation will be categorised as ambulatory-equivalent:

• the separation was a same day separation (that is, admission and separation occurred on the same day)
• the mode of admission did not include a care type change or transfer and the mode of separation did not include a transfer (to another facility), a care type change, the patient leaving against medical advice, or death.

References

AIHW (Australian Institute of Health and Welfare) (2002) Mental health services in Australia 1999–00, Mental health series no. 3. Cat. no. HSE 19, Australian Institute of Health and Welfare, Australian Government, accessed 17 February 2026.

AIHW (2003) Mental health services in Australia 2000–01, Mental health series no. 4. Cat. no. HSE 24, Australian Institute of Health and Welfare, Australian Government, accessed 17 February 2026.

Data presentation

Throughout this publication:

• Values presented in the columns and rows of tables may not sum to the totals shown due to missing and not stated values, as well as rounding
• Totals reported include missing and not stated values, unless otherwise noted.
• The percentages shown in the tables are calculated excluding the missing and not stated values, unless indicated otherwise
• Percentage distributions may not sum to 100 due to rounding
• The Australian Institute of Health and Welfare (AIHW) has strict confidentiality policies which have their basis in section 29 of the Australian Institute of Health and Welfare Act 1987 (AIHW Act) and the Privacy Act 1988 (Privacy Act). Data may be suppressed for either confidentiality reasons or where estimates are based on small numbers, resulting in low reliability. Information that results in attribute disclosure will be suppressed unless agreement from a particular jurisdiction or data custodian to publish the data has been obtained.
• Rates and percentages in data tables are rounded as integers
• Small numbers (value less than 5) in CSV files are rounded to the nearest 5 for the Community mental health care services section of the Mental Health Online Report.

Presentation of regional data

Data are reported at regional levels (for example, SA4 and PHN) for some of the datasets.

For the community mental health services, residential services, emergency departments, and admitted patients' sections of the Mental Health Online Report (MHOR), to report data at the SA4 level, data were aggregated to Statistical Areas 2 (SA2), and then converted to SA4 based on the correspondence files published by the Australian Bureau of Statistics (ABS). For years prior to 2017–18, the ABS Australian Statistical Geography Standard (ASGS) Edition 1 (2011) SA2 to SA4 concordance file was used. For data in years 2017–18 to 2021–22, the ASGS Edition 2 (2016) SA2 to SA4 concordance file was applied, and for years since 2022–23 (inclusive), ASGS Edition 3 (2021) concordance file was implemented to convert data from the SA2 level to SA4 level.

Data were mapped from SA2 to SA3 first by using the ABS ASGS SA2 to SA3 concordance files, and then from SA3 to PHN boundaries. For Admitted Care and Emergency Department Presentation, data up to year 2021–22 are mapped to 2017 PHN boundaries, and data for 2022–23 onwards are mapped to 2023 PHN boundaries.

For the Medicare Mental Health Services, Mental Health Prescriptions, and Expenditure sections of MHOR, patients postcodes sourced from the Medicare Enrolment File at the time of the latest claims processed were used to determine areas of usual residence. Data were summarised at the postcodes level and then concorded to SA4 by using the ABS ASGS Edition 3 (2021) correspondence file, and data at the postcode level were concorded to the PHN by using the Department of Health, Disability and Ageing Care Postal Areas to Primary Health Networks (PHN 2023) concordance file.

Population rates

In this publication, crude rates were calculated using the ABS estimated resident population (ERP) at the midpoint of the data range. For example, rates by sex and age groups for 2022–23 data were calculated using the ERP at 31 December 2022. Rates for Socio Economic Indexes Areas (SEIFA) and Remoteness Area (RA) were calculated using ERP at 30 June, the day before the referenced financial year.

Data for Victoria were not available for the 2011–12 and 2012–13 reporting periods for the Community mental health care section of the Mental health online report. Crude rates for national totals in this section were calculated by subtracting Victorian populations data from the National total. These population data were used in the denominator for calculating national ‘Total’ crude rates for these reporting periods.

Some data sources for the ACT were not available for the 2014–15, 2015–16, 2021–22 and/or 2022–23 reporting periods. Refer to the respective table footnotes for details. Crude rates for national totals in these sections were calculated by subtracting ACT populations data from the National total. These population data were used in the denominator for calculating national ‘Total’ crude rates.

Age-standardised rates

In this publication, some population rates are statistically adjusted (standardised) for age to facilitate better comparisons between populations that have different age structures, for example, between First Nations Australians and non-Indigenous Australians. This publication uses direct standardisation in which age-specific rates are applied to a standard population (the ERP as at 30 June 2001 unless otherwise specified). This effectively removes the influence of age structure on the calculated rate, that is known as the age-standardised rate. The method used for this calculation comprises 3 steps:

1. Calculate the crude age-specific rate for each 5-year age group
2. Calculate the expected number of cases in each 5-year age group by multiplying the age‑specific rates by the corresponding standard population and dividing by the base number for the rate calculation (for example 100,000), giving the expected number of cases
3. Sum the expected number of cases in each age group to give the
   age-standardised total expected number. Divide this sum by the total of the standard population and multiply by the applicable base number (100,000 in this example).

In some instances in this publication where the numbers in particular 5-year age groups are very small (less than 5), neighbouring age groups have been combined to enable the calculation of a meaningful crude rate.

Data for Victoria were not available for the 2011–12 and 2012–13 reporting period for the Community mental health care section of the Mental health online report. Age-standardised rates for this section were calculated with Victorian population data excluded from the national total.

Some data for the ACT were not available for the 2014–15, 2015–16, 2021–22 and/or 2022–23 reporting periods. Refer to the respective table footnotes for details. Age-standardised rates for these sections were calculated excluding ACT population data.

Average annual rates of change

In this publication, the average annual rates of change or growth rates have been calculated as geometric rates:

Average rate of change = ((P_n/P_o)^(1/n) -1) x 100

where:
P_n= value in the later time period
P_o= value in the earlier time period
n = number of years between the 2 time periods.

Average annual rates of change are not calculated where data are incomplete.

Confidence intervals

A confidence interval is a range of values that is used to statistically describe the uncertainty around an estimate, usually from a sample survey. Generally speaking, confidence intervals describe how different the estimate could have been if the underlying conditions stayed the same but variability in sampling, such as selecting a different sample from the population, had led to a different set of data. Confidence intervals are calculated with a stated probability (commonly 95%); this means that there is a 95% chance that the confidence interval includes the true value.

Indirect expenditure

The National Mental Health Establishments Database collects information on direct and indirect recurrent expenditure. Direct recurrent expenditure comprises salaries and wages and selected non-salary expenditure and is collected at the individual mental health service unit level.

Indirect recurrent expenditure is additional expenditure associated with the provision of mental health services not incurred or reported at the individual service unit level. Indirect expenditure is reported at 3 overarching levels above the individual service unit level:

• the organisational level; an organisation may or may not comprise a number of individual service units
• the regional level
• the state/territory level.

Some of these indirect expenditure items can be directly linked to the provision of services by the service units. Specifically, at the organisational and regional levels the expenditure on the following items is directly related to individual mental health service units and thus has been apportioned to units in the organisation or region reporting the indirect funds:

• program administration
• support services
• academic chairs
• superannuation
• workers compensation
• insurance
• patient transport services
• property leasing
• other indirect expenditure.

The apportioning of indirect expenditure is calculated on the total direct funds for the service, as a proportion of the total for all service units in the organisation or region. The total allocation or apportioning of funds is reported in the indirect expenditure rows in Table EXP.6.

The remaining indirect expenditure categories of education and training, research, mental health promotion, service development costs associated with the start up of new services and costs associated with the establishment and operation of jurisdictional Mental Health Act review bodies are not apportioned to mental health service units. State and territory level expenditure is also not apportioned to mental health service units. The total for these residual categories is reported in the row 'Other indirect expenditure' in Table EXP.6. Note that grants to non-government-organisations are not regarded as indirect expenditure.

Deflators

Expenditure aggregates in this report are expressed in current prices and/or constant prices. The transformation of current prices to constant prices is termed 'deflation', using price indexes or 'deflators'. There are a variety of deflators that can be used to translate current prices into constant prices. The deflators that were used by AIHW for the various items in the Expenditure on mental health services section are outlined in the table below. For further information on the methodology used to calculate deflators, refer to Health expenditure Australia 2023–24 (AIHW 2025).

1. Public hospital services exclude certain services provided in hospitals, and can include services provided off site, such as hospital in the home and dialysis.
2. 'Other' includes recurrent health spending that could not be allocated to a specific area of spending. For example, spending by substance abuse treatment centres, providers of general health administration, or providers of regional health services not further defined.

Reference

Australian Institute of Health and Welfare (AIHW) 2024. Concepts and definitions, Health expenditure Australia 2023–24. AIHW, Australian Government, accessed 17 February 2026.