Analysis
The Australian ERP as at 30 June 2001 is used as the standardising population throughout the report. Age‑standardisation of rates enables valid comparison across years and/or jurisdictions without being affected by differences in age distributions.
Population‑based rates of injury tend to have similar values from one year to the next. Exceptions to this can occur (for example, due to a mass‑casualty disaster), but are unusual in Australian injury data. Some year‑on‑year variation and short‑run fluctuations are to be expected, so small changes in a rate over a short period do not provide a firm basis for asserting that a trend is present.
All rate calculations utilise a denominator based on the estimated resident population (ERP) calculated as at the midpoint of each financial year. For example, for the reporting period 2021–22, the denominator population is the June 2021 ERP + the June 2022 ERP, divided by 2. This is used as the denominator for age specific/crude and age standardised rates. Rates are calculated for each financial year unless otherwise noted.
Common measure calculations are outlined in Table 2.
| Measure | Numerator | Denominator | Calculation |
|---|---|---|---|
Population (used for rates) | June 21 population + June 2022 population | 2 | Numerator ÷ Denominator |
| Crude or age-specific rate of hospitalisation | Number of cases of injury hospitalisation per defined category (for example, age group) | Estimated Australian population as at mid-point of financial year | (Numerator ÷ Denominator) x 100,000 |
Age-standardised rate (ASR). Age-standardised rates were derived using 5-year age groups up to 85+. Age-standardised rates for First Nation populations were derived using 5-year age groups up to 65+. | Expected events per age group in standard population= crude rate of hospitalisation x standard population (for each corresponding age group) | The direct method of standardisation is used. (Sum of numerators across all age groups ÷ total standard population) x 100,000 | |
Average length of stay | Number of patient bed days | Number of cases | Numerator ÷ Denominator, as days, rounded to 1 decimal place |
Change in rates | Sum of rate changes | Number of years | Estimated trends in age-standardised rates were reported as average annual percentage changes. |
| Rate ratios | Crude rate of hospitalisations for a defined age group among children | Crude rate of hospitalisations among adults | Numerator ÷ Denominator |
| Crude rates of sports injuries | Number of cases of injury hospitalisation per defined category (e.g. age group) | AusPlay Participant estimate data for the given financial year | (Numerator ÷ Denominator) x 100,000 |
Note that ‘average length of stay’, as presented in this report, does not include some patient days potentially attributable to injury. It does not include days for most aspects of injury rehabilitation, which cannot be reliably assigned without information enabling identification of all admitted episodes associated with an injury case.
Due to rounding, percentages in tables may not add up to 100.0.
Remoteness is based off the patient’s usual place of residence. Remoteness areas in Australia are comprised of 5 groups (Major cities, Inner regional, Outer regional, Remote, and Very remote) categorised by the Accessibility/Remoteness Index of Australia Plus (ARIA+). These ARIA+ values are derived using the Statistical Area Level 1 (SA1) from the Australian Statistical Geography Standard (ASGS) 2016.
| Remoteness area | Average ARIA+ range for SA1 |
|---|---|
| Major cities of Australia | 0 to 0.2 |
| Inner regional Australia | Greater than 0.2 and less than or equal to 2.4 |
| Outer regional Australia | Greater than 2.4 and less than or equal to 5.9 |
| Remote Australia | Greater than 5.92 and less than or equal to 10.53 |
| Very remote Australia | Greater than 10.53 |
Counts are presented as whole numbers.
Crude/age-specific rates and age-standardised rates are calculated per 100,000 population and are rounded to 1 decimal place.
Proportions (%) that are less than 10% and ALOS are also rounded to 1 decimal place.
Aggregated injury hospitalisations data are usually presented in tables, graphs, or maps. To maintain attribute disclosure and minimise risk of potentially re-identifying a person, data suppression rules have been applied.
Sometimes consequential suppression is also applied to prevent the primary suppressed cell from being calculated. This is often done by suppressing table cells in the same row or column or suppressing the table totals.
Counts (hospitalisations):
- Counts less than 5 are suppressed and consequential suppression is applied unless that count applies to a whole of population level, in which case it may be published unsuppressed if there is not further ability to disaggregate by population groups.
- When data is disaggregated by geography location, counts for areas where the population is less than 1,000 are suppressed.
Crude rates:
- Crude rates with counts (numerator for calculation) less than 10 are suppressed.
- If the corresponding counts measure is suppressed, the crude rate has been suppressed.
- When data is disaggregated by geography location, counts for areas where the population is less than 1,000 are suppressed.
- Age-standardised rates:
- Age-standardised rates with counts (numerator for calculation) less than 20 are suppressed
- If the corresponding counts measure is suppressed, the age-standardised rate has been suppressed.
- When data is disaggregated by geography location, counts for areas where the population is less than 30 are suppressed.