Aboriginal and Torres Strait Islander people represented around 3% of the Australian population in 2016 and have an age structure which is notably younger than for the Australian population overall.¹ When examining data for Aboriginal and Torres Strait Islander people, data is presented using age standardisation ratios for Aboriginal and Torres Strait Islander peoples. The ratios are calculated by dividing the number of observed separations by the number that would have been expected from the same age-specific rates (those for the total population). These ratios are multiplied by the common crude rate for the total population to give the indirectly standardised rates.  

Due to the smaller population size and therefore the numbers of procedures for Aboriginal and Torres Strait Islander people, this analysis shows indirectly age-standardised ratios for key selected surgical procedures for admitted patients with a principal diagnosis of the relevant cancer for the five-year period between 2011 and 2015. Indirectly age-standardised rates are presented for Aboriginal and Torres Strait Islander people.

This measure shows the distribution of hospital separations for key selected surgical procedures (see list below), for admitted patients with a principal diagnosis of the relevant cancer between 2011 and 2015.

Unit of analysis:

Expected separations and indirectly age standardised rates are calculated from the number of hospital separations observed where the principal diagnosis for a relevant cancer were recorded and where at least one cancer-related procedure listed below was performed. This section presents the following measures for Indigenous Australians and other Australians:​

• Indirectly age standardised separations’ rates
• Ratios of indirectly age standardised separation rates to directly age standardised cancer incidence rates

In this data summary, ratios of indirectly age-standardised separations rates and directly age-standardised cancer incidence rates are presented. Directly age-standardised incidence rates were sourced from the AIHW Cancer in Australia 2017 and include cancer diagnoses from all jurisdictions. Ratios of standardised separation and incidence rates presented will therefore be a slight underestimate of the true figure as separation data from the NHMD by Indigenous status are not available for the Australian Capital Territory and Tasmania. The unavailable data for these jurisdictions is not expected to have a large effect on the separation to incidence ratios as Aboriginal and Torres Strait Islander people in Australian Capital Territory and Tasmania account for a relatively small proportion (<5% in 2016) of all Aboriginal and Torres Strait Islander people.¹

For comparison, indirectly age-standardised incidence rates were calculated and there were no notable differences in the rates (and rate ratios) calculated using the direct or indirect method.

Data source:

The data for this measure are sourced from the AIHW National Hospital Morbidity Database (NHMD). The AIHW NHMD is a compilation of episode-level records from admitted patient morbidity data collection systems in Australian hospitals. The data supplied are based on the National Minimum Data Set (NMDS) for Admitted patient care; they include demographic, administrative and length of stay data, as well as data on the diagnoses of the patients, the procedures they underwent in hospital and external causes of injury and poisoning.

The scope of the NMDS 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. Hospitals operated by the Australian Defence Force, corrections authorities and in Australia’s off-shore territories are not in scope, but some are included.²

More information about the NHMD and definitions used can be found in Appendices A and B of Admitted patient care 2015-16: Australian hospital statistics.²

Age standardised cancer incidence rates were sourced from the AIHW Cancer in Australia 2017: Chapter 8, Key population groups supplementary tables.³

Methodology for age standardisation (indirect):

Age standardisation refers to a method of adjusting for differences in age structure when comparing different populations. This is often necessary as diagnosis and separation rates are strongly related to age. There are two methods for calculating age standardised rates: direct and indirect standardisation.

For this indicator, the indirect method was used to calculate age standardised separation rates. Indirectly age standardised rates (ASR_(ind)) were calculated as the weighted average of the age-specific rate ratios, where the weights are the expected number of separations on each age group of the population being compared⁴:

Where:

ASR(ind) = Indirect age standardised rate

d = The observed number of separations for the comparison population (Indigenous/Other Australians)

i = Age groups used for standardisation

Σ(R_in_i) = Expected number of separations

R_i = Age-group specific rate in age group i for the standard population

n_i = Population in age group i for the comparison population(Indigenous/Other Australians)

R = Crude rate for standard population (per 100,000 persons)

Age standardised separation ratios are based on the aggregated number of separations for the 2011 to 2015, inclusive. For the purposes of this calculation, the age groups used for standardisation were: 0-39 years, 40-44 years, 45-54 years, 55-59 years, 60-64 years, 65-69, 70-74 years, 75 years and over.

Note: Direct age standardisation was not a suitable method for the present data due to the small number of hospital separations (<25) for some Indigenous Australian age groups for key selected surgical procedures with a principal diagnosis of cancer. Calculation of directly age standardised rates using the available data was not considered to be reliable for reporting purposes.⁴ Selection of the standard population as all Australians (instead of other Australians) was considered to be appropriate as Aboriginal and Torres Strait Islander peoples accounted for a relatively small proportion of all Australians (<3%).¹

For these analyses, confidence intervals have not been included due to lack of independence between observations. 

Admitted patient procedures:

Some admitted patient procedures included may have been diagnostic for a particular cancer rather than a specific treatment for the cancer. The following procedure codes defined by the Australian Classification of Health Interventions (ACHI) 6th-8th edition were included in the analysis. The ACHI is based on the Medicare Benefits Schedule (MBS) and was developed by the National Centre for Classification in Health (NCCH). For further information on the ACHI please refer to the Australian Consortium for Classification and Development website.

* For breast cancer related hospital separations, “breast reconstruction” procedures have not been included as these may not necessarily be intended for the treatment of breast cancer

** The lung cancer admitted patient procedures “pleurectomy” (38424-00) and “excision of lesion” (41892-01, 41901-00) are not intended to treat lung cancer directly and are intended for symptom relief or palliative care.

***The prostate cancer procedures “Transurethral resection of the prostate” (37203-00), “Radical prostatectomy (NOS)” (37209-00), and “Laparoscopic radical prostatectomy (NOS)” (37209-01) are procedures that may result in the diagnosis of prostate cancer and are not a specific treatment for prostate cancer.

Further information on the data excluded from the analysis is available at ‘About the data’ on the Surgical treatment activity page on the NCCI website

Data caveats:​

• NHMD data on Indigenous status are considered to be of sufficient quality for analysis purposes for New South Wales, Victoria, Queensland, South Australia, Western Australia and the Northern Territory (public hospitals only).
• “Other Australians” includes separations for which Indigenous status was not reported.
• Data for “Laparoscopic right hemicolectomy with anastomosis” procedures (ACHI code 32003-03) with a principal diagnosis of colorectal cancer (C18-C20) were unavailable by Indigenous status. To allow for comparisons between these groups to the standard population (all Australians), these procedures have also been excluded from the number separations for the standard population.
• Expected number of separations and separation rates were obtained by applying standard age-specific rates for the reference population to the age-distributions of the relevant groups being studied (Indigenous and other Australians).
• Directly age standardised incidence rates were sourced from the AIHW Cancer in Australia 2017 and include cancer diagnoses from all jurisdictions. Rate ratios will therefore be an underestimate of the true figure as separation data from the NHMD by Indigenous status are not available for the Australian Capital Territory and Tasmania.