Measuring cancer in Indigenous populations

A recent symposium held in Wellington, New Zealand, brought experts together from across the region with the aim of providing an accurate and up-to-date picture of how cancer impacts on the Indigenous peoples of Australia, New Zealand and the Pacific.

One of the issues under discussion was how best to measure this impact.

In the post below, three of the authors of a recent paper on this topic, Indigenous health epidemiology and cancer researchers Dr Kalinda Griffiths, Dr Suzanne Moore and Professor Gail Garvey, explain why cancer surveillance in Indigenous populations can be prone to several sources of bias.

They also provide advice on the ethical collection and use of accurate data, with the aim of reducing the burden of cancer in Indigenous populations, both worldwide and in Australia.

Dr Kalinda Griffiths, Dr Suzanne Moore and Professor Gail Garvey write:

Around the globe, cancer is a leading cause of reported deaths for Indigenous peoples. To estimate the impact of cancer on a population, the measurements of incidence, survival and mortality are used as the foundation of cancer surveillance.

Cancer surveillance provides information for monitoring trends, planning and evaluating cancer services, allocating spending on resources, and guiding overarching priorities in cancer control.

Within the Indigenous context, there are a range of measurement problems that need to be addressed to ensure quality data and accurate estimates of cancer measures. These problems include inaccuracies in the recording of indigenous people, numerator-denominator bias, and data linkage and statistical approaches.

There are also ethical and value issues, particular to each country, that need to be discussed when using data pertaining to Indigenous people.

In a new paper published in the Annals of Epidemiology, we aimed to address some of these measurement issues in global Indigenous cancer surveillance.  Here we explore some issues that Indigenous people, researchers, policy makers and others involved in the surveillance of cancer in Indigenous Australians need to consider.

Indigenous identification and numerator/denominator bias

Most nations do not have Indigenous identifiers in their cancer registries and the quality of Indigenous identification reporting also varies from country to country. This can impact estimates of cancer measurements.

The magnitude of the impact in the cancer estimates depends on the following:

1) Variations in how Indigenous status is recorded and reported;

2) How many Indigenous people are missed; and

3) The size of the gap between those Indigenous people who are missed, from those who are counted.

To estimate cancer measurements of incidence, survival and mortality in Indigenous populations, Indigenous people need to be identified across three primary datasets – namely cancer registries, mortality statistics, and census data.

Inaccuracies in the counts of Indigenous people in the different datasets can lead to numerator (including data from the cancer registry, or from the mortality data) and denominator (from census data) bias.

So, if there are variations in the ways in which Indigenous people are identified in the datasets, there can be substantial bias that needs to be assessed and accounted for. For clarity, bias includes any deviation of results or inferences from the truth (Last, 2001, page 21).

In Australia, as in New Zealand, cancer registry data on Indigenous people is derived from health services data. Indigenous people can choose whether or not to identify as Indigenous when they attend their health services. This approach aligns with the United Nations Declaration on the Rights of Indigenous People (UNDRIP) Article 33 that states, ‘Indigenous peoples have the right to determine their own identity or membership in accordance with their customs and traditions.’

It is important to recognise that there are specific reasons intertwined in systemic processes, historical legacies, trust and respect, that individuals may choose to, or choose not to, identify within health services.

To accurately identify Indigenous people in data pertaining to health measurement, there needs to be a provision to enable people to choose to identify, and also to ensure that factors that can contribute to reasons for non-identification are recognised, acknowledged and actioned appropriately.

Cancer and Indigenous people in Australia

The story for cancer and Indigenous people in Australia parallels the global picture. Specifically, cancer is the third leading cause of death for Indigenous people in Australia and we are, on average, about 30% more likely to die from cancer than our non-Indigenous counterparts.

There have been significant improvements towards addressing cancer and cancer disparities experienced by Indigenous people in Australia, although there is still much to be done to reach parity. Evidence-based recommendations for national Indigenous cancer control were published in a 2010, Cancer Australia Report.

Since then, other important developments have included the nationally agreed, ‘The National Aboriginal and Torres Strait Islander Cancer Framework’. Its purpose is to address disparities and improve outcomes for Indigenous people in Australia by guiding cancer control efforts.

To connect stakeholders in Indigenous cancer control and to share information on cancer, the National Indigenous Cancer Network (NICaN) was established in 2015 as part of the broader Indigenous Health Information Net.

More recently, a draft for a national ‘Optimal Care Pathway for Aboriginal and Torres Strait Islander People’ has been circulated by Cancer Australia. The aim of the document is to map the cancer pathway of specific tumours, and to provide a template for evaluating cancer care programs with a focus on the promotion of quality cancer care and patient experiences.

Considerations in the use of cancer data pertaining to Indigenous people

Population level data can be an incredibly useful resource. Data are required to describe disparities in cancer. Using data we can measure prevalence, incidence, survival and mortality from all or selected cancers. We can also monitor trends and treatment outcomes to see what programs and services are working, or what is not working.

The importance of quality and complete data in measuring cancer in Indigenous populations is vital if we are to address disparities in cancer outcomes.  In fact, the need for better data was noted by a number of speakers at the recent symposium, Indigenous People and Cancer: A shared agenda for Aotearoa, Australia and the Pacific Nations held on the 19-20 February 2018 (see feature image above).

Any discussion about the use of cancer data pertaining to Indigenous people requires a conversation that includes data sovereignty. There is a wider need for focused development around how to apply principles of data sovereignty and to also develop data governance within governments and institutions.

This is to ensure not just that researchers and data custodians are working together with Indigenous people and communities, but that Indigenous people and communities are setting priorities and developing the best ways forward in cancer research and programs that impact them.

This idea for Indigenous led-approaches in ensuring self-determination is strengthened by Article 23 of the UNDRIP which states that, “Indigenous people have the rights to determine and develop priorities and strategies for exercising their right to development.”

Accurate measurement of cancer is vital to address cancer disparities in Indigenous populations but strong Indigenous leadership and strong partnerships are critical components in future directions.

*Dr Kalinda Griffiths is a research fellow at the Sydney Centre for Aboriginal and Torres Strait Islander Statistics, University of Sydney and honorary fellow, Wellbeing and Preventable Chronic Disease Division, Menzies School of Health Research. On twitter @Klick22 . Dr Suzanne Moore is a research fellow, Wellbeing and Preventable Chronic Diseases Division, Menzies School of Health Research, Brisbane. Professor Gail Garvey is Deputy Division leader, Wellbeing and Preventable Chronic Diseases Division, Menzies School of Health Research, Brisbane.