Fourth Atlas 2021 - How to interpret the data

The data in the Atlas show the rates for featured procedures, investigations, treatments or hospitalisations in each geographic area. To calculate rates, the number of interventions that occurred in an area is divided by the population of that area.

Why are the data age standardised and sex standardised?

Rates are age and sex standardised to account for differences in age and sex structure of local populations, and enable comparison across areas. Without age standardisation, it would be difficult to know whether higher rates of an intervention in an area with a large number of retirees, for example, were due only to the older age of the local population. Similarly, sex standardisation means a larger proportion of males or females in one area does not influence the findings.

Rates are based on the patient’s place of usual residence and not where the service was provided. The early planned births (caesarean or induction) indicators are not age standardised because of small numbers.

Magnitude of variation

The magnitude of variation shows how large the difference is between the lowest and highest rates of each intervention. This is expressed as a ratio of the highest to the lowest rates. For example, if the lowest rate was 10 per 100,000 people and the highest rate was 20 per 100,000 people, the magnitude of variation is two‑fold.

Australian rate

Rates for an intervention may appear higher or lower than the Australian rate. In most cases, the most appropriate rate is difficult to define and not necessarily the Australian rate. An Australian rate is provided to encourage investigation into the reasons for any variation seen at local, regional, or state and territory levels.

About the data

The fourth Atlas uses data from four national health datasets, depending on the clinical item:

  • Medicare Benefits Schedule (MBS) items are analysed for services provided in 2018–19
  • National Hospital Morbidity Database (NHMD) items are analysed for hospitalisations in

– 2014–15 to 2017–18 for potentially preventable hospitalisations

– 2012–13 to 2014–15 and 2015–16 to 2017–18 for lumbar spinal surgery items, which are analysed for three combined years because of small numbers

– 2012–13, 2015–16 and 2017–18 for ear, nose and throat surgery items

  • The National Perinatal Data Collection (NPDC) item is analysed for early planned births (caesarean or induction) in 2017
  • PBS items are analysed for prescriptions dispensed in 2018–19.

For further information, see the About the Atlas section of the Fourth Atlas or learn more about using the interactive maps and graphs.