Patterns of mortality in Indigenous adults in the Northern Territory, 1998–2003

In reply: We thank Zhao and colleagues for their interest in our study.1 The main issue they raise is misclassification of deaths by remoteness of residence. In our article, we acknowledged the role of migration to larger urban centres to access health services and raised the issue of unhealthy lifestyle and its flow-on effects on mortality.

If we were to assume that 26% of deaths in hospital in remote areas were deaths of people who previously lived in very remote areas (as Zhao and colleagues suggest), regional variation in the disparity between Indigenous and total Australian all-cause mortality would narrow but would still remain. A re-analysis of our data based on this assumption1 shows that standardised mortality ratios in remote areas would drop from 875% (95% CI, 799%–956%) to 646% (95% CI, 582%–717%) in 1998–2000 and from 731% (95% CI, 665%–801%) to 540% (95% CI, 484%–601%) in 2001–2003. In very remote areas, the standardised mortality ratios would increase from 214% (95% CI, 193%–236%) to 281% (95% CI, 258%–306%) in 1998–2000 and from 208% (95% CI, 189%–228%) to 264% (95% CI, 242%–286%) in 2001–2003.

Furthermore, in our article we stressed the importance of examining Indigenous migration to enable more accurate interpretation of our findings and called for future studies to “clarify the reasons for these differences in mortality by remoteness, with a particular focus on migration”.

Our studies of Queensland data and national data (unpublished) have shown a similar pattern of higher Indigenous mortality in remote areas than in very remote areas, but the difference in mortality rates between these areas is highest in the Northern Territory. Thus, the phenomenon of the “methodological” error applies to all of these studies.

We propose to undertake a prospective study of Indigenous mortality that will overcome some study design problems inherent in a cross-sectional study.