Data sources, classifications and methods
This section outlines the data source, classifications and methods for analysing the data presented in the Atrial Fibrillation in Australia web report.
The National Hospital Morbidity Database (NHMD) is a collection of episode-level records from the Admitted Patient Care National Minimum Data Set. It contains information on episodes of care for admitted patients in hospital, and includes demographic, diagnostic, outcomes, interventions and procedural information.
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.
The counting unit in the NHMD is the ‘separation’, described as ‘hospitalisations’ in this report. ‘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 following care types were excluded from analysis: 7.3 (newborn—unqualified days only), 9 (organ procurement—posthumous) and 10 (hospital boarder). Separations from Western Australia which were coded as being an ‘Inter-hospital contracted patient to private sector hospital’ were excluded based on advice from WA to avoid double counting of these separations.
This report includes analysis of hospitalisations in which AF was coded as a principal diagnosis and additional diagnosis.
- A principal diagnosis is recorded at separation and determined to be chiefly responsible for the patient's episode of care in hospital.
- An additional diagnosis is a condition or complaint either coexisting with the principal diagnosis or arising during the episode of admitted patient care. An additional diagnosis is reported if the condition affects patient management.
Analysis of procedures is included in this report.
- A procedure is a clinical intervention that is surgical in nature, carries a procedural risk, carries an anaesthetic risk, requires specialised training and/or requires special facilities or equipment available only in an acute-care setting.
The National Mortality Database (NMD) contains Cause of Death Unit Record File data provided to the AIHW by the Registries of Births, Deaths and Marriages and the National Coronial Information System (managed by the Victorian Department of Justice) and include cause of death coded by the Australian Bureau of Statistics (ABS). The data are maintained by the AIHW in the NMD.
Deaths registered in 2015 and earlier are based on the final version of cause of death data; deaths registered in 2016 are based on a revised version; and deaths registered in 2017 and 2018 are based on a preliminary version. Revised and preliminary versions are subject to further revision by the ABS.
Mortality data by Indigenous status are reported for 5 jurisdictions combined: New South Wales, Queensland, Western Australia, South Australia and the Northern Territory. The AIHW considers the quality of Indigenous identification in mortality data for these 5 jurisdictions to be adequate from 1998.
The analysis using the NMD includes deaths with AF listed as the underlying cause and listed as an associated cause:
- Underlying cause of death is the condition, disease or injury that initiated the sequence of events leading directly to death; that is, the primary or main cause. For each death, only a single underlying cause is selected from all the conditions reported on a death certificate.
- Associated causes of death are all causes listed on the death certificate, other than the underlying cause of death. They include the immediate cause, any intervening causes, and conditions that contributed to the death but were not related to the disease or condition causing the death.
AF was classified in the NHMD using the International statistical classification of diseases and related health problems 10th Revision, Australian Modification (ICD-10-AM, 10th edition, ACCD 2019a) using code I48, and in the NMD as ICD-10 code I48.
Stroke was classified in the NHMD as (ICD-10-AM, 10th edition) codes I60–I64, and in the NMD as ICD-10 codes I60–I64.
The Australian Classification of Health Interventions (ACHI) procedure codes used in analysis of hospitalisations with the principal diagnosis of AF are presented in Table 1.
|ACHI procedure code (block number)||Description|
Electric countershock of heartRestoration of cardiac rhythm by electrical stimulation
|Cardiac ablation||Block: 601||Destruction procedures on atrium|
|Cardiac ablation (in ACHI 4th and 5th editions only)||38212-01 (Block: 665)||
Cardiac electrophysiological study with radiofrequency ablation
The procedure rate presented in this report is the number of hospitalisations in which AF was the principal diagnosis and the procedure of interest was undertaken, expressed as a rate per 100 hospitalisations in which AF was the principal diagnosis. Procedures or groupings of procedures were counted once only, regardless of whether the same procedure or grouping of procedures was conducted more than once in a hospitalisation.
Age-specific rates are calculated by dividing the number of cases occurring in a specified age group by the corresponding population in the same age group, expressed as a rate (for example, number per 100,000 population).
Age-standardisation is a method of removing the influence of age when comparing populations with different age structures—either different populations at one time or the same population at different times. Direct age-standardisation was used in this report. The Australian estimated resident population as at 30 June 2001 has been used as the standard population.
A rate ratio provides a measure of the relative difference in rates between 2 populations. A rate ratio of 1 indicates no difference in the rates between the populations; less than 1 indicates that the rate for population A (for example, females) is lower than that for population B (for example, males); and greater than 1 indicates that the rate for population A is higher than that for population B.
This report presents trend data on AF hospitalisation, including procedures, and on death rates using data from the AIHW NHMD (for 2000–01 to 2017–18) and the NMD (from 2001 through to 2018). Age-standardised rates for hospitalisation and death rates, and the percentages of all death and all hospitalisations are presented for this time period. The percentage of change is calculated as the difference between the values of the first and last time periods, divided by the value in the first time period.
Comparisons of regions in this report use the ABS Australian Statistical Geography Standard (ASGS) 2016 Remoteness Structure, which groups Australian regions into 6 remoteness areas. The 6 remoteness areas are Major cities, Inner regional, Outer regional, Remote, Very remote and Migratory. These areas are defined using the Accessibility/Remoteness Index for Australia (ARIA), which is a measure of the remoteness of a location from the services that large towns or cities provide.
Further information on the ASGS is available on the ABS website.
Socioeconomic classifications in this report are based on the ABS Index of Relative Socio-economic Disadvantage (IRSD). Geographic areas are assigned a score based on social and economic characteristics of that area, such as income, educational attainment, public sector housing, unemployment and jobs in low-skill occupations. The IRSD relates to the average disadvantage of all people living in a geographical area. It cannot be presumed to apply to all individuals living in the area.
For the analyses in this report, the population is divided into 5 socioeconomic groups, with roughly equal populations (each around 20% of the total), based on the level of disadvantage of the statistical local area of their usual residence. The first group includes the 20% of the population living in areas with the highest levels of relative disadvantage (referred to as Group 1, most disadvantaged), while the last group includes the 20% of the population living in areas with the lowest levels of relative disadvantage (referred to as Group 5, least disadvantaged).
The IRSD values used in this report are based on the 2016 Census. Further information is available on the ABS website.
Aboriginal and Torres Strait Islander persons
In this report, comparisons are made between Aboriginal and Torres Strait Islander persons and people who do not identify as Indigenous.
People with ‘not-stated’ Indigenous status are excluded from any analysis by Indigenous status.
ACCD (Australian Consortium for Classification Development) 2019a. International statistical classification of diseases and related health problems, 10th Revision, Australian Modification (ICD-10-AM), 10th edition. Tabular list of diseases, and alphabetic index of diseases. Adelaide: Independent Hospital Pricing Authority.
ACCD 2019b. The Australian Classification of Health Interventions (ACHI), 10th edition. Tabular list of interventions, and alphabetic index of interventions. Adelaide: Independent Hospital Pricing Authority.