About the data
Hospitals data
Potentially preventable hospitalisations (PPH) data were sourced from the National Hospital Morbidity Database (NHMD), held by the Australian Institute of Health and Welfare, covering admitted patient care from 1 June 2011 to 30 July 2024. Hospitalisations classified as potentially preventable according to the National Healthcare Agreement 2024 definitions (see National Healthcare Agreement: PI 18–Selected potentially preventable hospitalisations, 2024) are included in the analysis.
- The unit of measurement is episodes of care, defined by the financial year of separation (when a patient’s episode of care is completed). This includes a full hospital stay (ending in discharge, transfer, or death) or a partial stay if the care type changes (for example, from acute to rehabilitation). Each hospitalisation generates a record, so patients with multiple hospitalisations or transfers within a financial year will have multiple records.
- Exclusions include episodes for unqualified newborn care, posthumous organ procurement, hospital boarders, and cases with missing age data.
- For further details on data quality and changes in coding practices over time, refer to Admitted Patient Care 2021–22: Data Quality Statements.
Population data
Population counts used in this report are based on Estimated Resident Populations (ERPs) for national, regional, and First Nations populations, as of 30 June of each calendar year, sourced from the AIHW reference database. For the purposes of this report, population estimates are applied as of 31 December of each calendar year to align with the midpoint of the financial year data (for example, 2021–22, 2022–23). These centred population estimates are interpolated by calculating the implied population growth between the 30 June estimates of consecutive years. For example, the population for 31 December 2021 is estimated as the midpoint between the ABS ERPs for 30 June 2021 and 30 June 2022, assuming steady growth.
First Nations Population
A significant increase in First Nations identification was observed in the 2021 ABS Census. This increase may artificially lower PPH rates for First Nations populations in recent years, as the denominator (population size) has grown more than expected compared to prior years.
Trends for First Nations people in this report are calculated using population estimates and projections based on the 2021 Census. Trends are limited to 2016 onwards, due to a large non-demographic increase in Census counts of Aboriginal and Torres Strait Islander people between 2016 and 2021. The rates for Aboriginal and Torres Strait Islander people in this report are generally lower than, and are not comparable to, those in previous reports.
For further information, see Understanding change in counts of Aboriginal and Torres Strait Islander people and Guide to using historical estimates for comparative analysis and reporting.
Age standardisation
Age standardised rates are hypothetical rates that would have been observed if the populations studied had the same age distribution. This facilitates comparisons between populations with different age structures and changes over time within an area. This adjustment is important because the prevalence of health conditions and rates of health service use vary with age.
Age standardised rates were derived by calculating crude rates by five-year age groupings of 0–4 years to 85+ years. These crude rates were then given a weight that reflected the age composition of the standard population (ABS ERP for Australia as of 30 June 2001).
Geography
The report presents data at national and sub-national geographic levels, disaggregated by:
- State and Territory
- Remoteness Areas (RA)
- Socio-Economic Indexes for Areas (SEIFA)
SEIFA geography is based on the area of usual residence as recorded in the National Hospital Morbidity Database.
RA have changed over time. This report uses 2024 concordances based on the 2021 Australian Statistical Geography Standard (ASGS) and 2021 Census population data.
National totals include data where place of usual residence was overseas, no fixed abode, offshore and migratory, and undefined. These records are excluded from remoteness areas (RA) and Socio-Economic Indexes for Areas (SEIFA) estimates. National totals may not match the sum of sub-national geographies because correspondences used to map to RA and SEIFA can introduce small errors that result in discrepancies.
Remoteness areas
Data for remoteness areas are based on a person’s usual residence as recorded in the National Hospital Morbidity Database (NHMD), rather than the location where they died (as in the National Mortality Database, NMD) or received treatment (NHMD). The 2021 ASGS Remoteness Structure categorises geographic areas in Australia into five classes based on their relative access to services, using the Accessibility/Remoteness Index of Australia (ARIA+). The ARIA+ measures the road distance of a location from the nearest urban centre, with urban centres defined based on population size and service availability. The 5 classes are: Major cities, Inner regional, Outer regional, Remote, and Very remote.
Socioeconomic areas
The Socio-Economic Indexes for Areas (SEIFA) is a suite of four summary measures, developed by the ABS based on census data that ranks geographic areas across Australia in terms of their relative socioeconomic advantage and disadvantage. This report uses the SEIFA Index of Relative Socioeconomic Disadvantage (IRSD) by Statistical Area Level 2, 2021 with exception of the NHMD 2012–13 to 2016–17 data which uses the SEIFA 2011.
The IRSD includes only measures of relative disadvantage. A low score indicates greater disadvantage in general (for example, an area has many households with low income, many people with no qualifications and many people working in low skill occupations). A high score indicates a relative lack of disadvantage in general (for example, an area has few households with low incomes, few people with no qualifications and few people working in low skilled occupations). A high IRSD score indicates a relative lack of disadvantage (not advantage). The IRSD measures the average level of disadvantage for all people in an area, not the socioeconomic circumstances of each individual living there.
Population-based Australian cut-offs for SEIFA quintiles have been used in this report. Population-based quintiles divide ranked SEIFA scores into 5 approximately equal groups. As SEIFA measures the characteristics of an area rather than individuals, the population in the most disadvantaged population-based quintile (‘1–Lowest’) is the 20% of the national population residing in the most disadvantaged areas, rather than the most disadvantaged 20% of the population.
See the Census of Population and Housing: Socio-Economic Indexes for Areas (SEIFA) Australia, 2021 for further information on SEIFA.
Suppression and non-published results
Data for an area were suppressed and marked as ‘n.p.’ (not published) when the number of rounded hospitalisations was between 1 and 4. In addition, the number of hospitalisations for all jurisdictions was omitted from the report due to jurisdictional governance processes and indicated as ‘n.p.’.
First Nations terminology
The AIHW uses 'First Nations people' to refer to Aboriginal and/or Torres Strait Islander people in this report. However, the AIHW acknowledges First Nations peoples comprise hundreds of groups with distinct languages, histories, and cultural traditions and therefore the preferred terminology for the use of either Aboriginal, Aboriginal and/or Torres Strait Islander, First Nations people or other terminology may vary across jurisdictions.
Comparability with other publications
Results in this report may differ slightly from other publications. Differences can occur because of:
- variations in scope, such as inclusions and exclusions
- availability of more recent data
- back-casting methods
- treatment of records with missing data
- data suppression.
This report uses Socio-Economic Indexes for Areas (SEIFA) based on the area of usual residence recorded in the National Hospital Morbidity Database. It applies 2024 concordances based on the 2021 Australian Statistical Geography Standard (ASGS) and 2021 census population data. It also includes data from ‘other’ Australian states and territories.
Reports that use different geographic levels or correspondence methods may produce different results.