Socio-economic status half story in death rates

Monday 8 May 2006

Socio-economic status half the story in ethnic death rate differences

Both socio-economic status and other factors account for inequalities: New Report

Socio-economic factors account for about half of the widening gap in mortality between Māori and non-Māori during the 1980s and 1990s, new Otago research shows. The finding reinforces the need to take both socio-economic position and ethnicity into account in health funding formulas, the researchers say.

The research was released jointly today by the University of Otago and the Ministry of Health as the third and final Decades of Disparity report. It shows that approximately half of the over two-fold difference in death rates between Māori and non-Māori aged 25-59 is due to the greater socio-economic advantages of non-Māori.

“Inequalities in socioeconomic resources are an important cause of inequalities in mortality between Māori and non-Māori,” says co-author Associate Professor Tony Blakely. “In addition, things other than socio-economic resources are also important determinants of ethnic inequalities in health.”

In the first Decades of Disparity report released in 2003, Assoc Prof Blakely and co-author Bridget Robson, both of the University’s Wellington School of Medicine and Health Sciences, argued that “increasing Pākehā advantage in access to and power over socioeconomic resources is the primary cause of the widening gaps in mortality between Māori and Pākehā”.

“Though this statement generated a lot of debate at the time, the results of today’s report largely support this argument,” says Assoc Prof Blakely.

“Amongst socio-economic factors, we found that employment was a key explanatory variable,” explained Ms Robson, a member of the Wellington School’s Eru Pomare Māori Health Research Centre. “This fits with the large increases in unemployment in the late 1980s and early 1990s that impacted disproportionately upon Māori.”

Based on their findings, the researchers are calling for a sustained long-term commitment from Government to help reduce socio-economic inequalities between ethnic groups.

“We need to take the longer view because, quite frankly, improvements in health and mortality don’t just happen over night – it takes time for improved socio-economic circumstances to have an impact,” says Assoc Prof Blakely. “That’s why we’re looking for a sustained political commitment not just from the present Government but from successive governments to ensure that both ethnicity and socio-economic status continue to factor in the funding of health programmes.”

About half of ethnic disparities in mortality were not explained by socio-economic status as measured by this study.

Possible factors behind this component of the disparities include: unequal access to, and access through, health services; different exposures to healthy or disease producing environments (such as good quality housing, stressful situations, smoking, exercise); and early childhood and early life experiences. Disparities in these factors, and in socioeconomic status itself, are underpinned by historical and social processes that systematically disadvantage Māori (ie, colonisation, discrimination and racism).

As ethnicity is not a measure of genetics, individual genetic risks are unlikely to directly explain a substantial proportion of differences in all-cause mortality between Māori and non- Māori at the population level.

The report is a joint report between the researchers at the University’s Wellington School of Medicine and Health Sciences and the Ministry of Health. The New Zealand Census Mortality Study (NZCMS), from which the work arose, was previously funded by the Health Research Council of New Zealand and now funded by the Ministry of Health and University of Otago. The NZCMS is conducted in collaboration with Statistics New Zealand.

SUPPORTING INFORMATION

Key findings from the report
1. Māori were disproportionately represented in lower socioeconomic strata (eg, lower income, no qualifications, no car access) during the 1980s and 1990s, however measured. As a consequence, Māori are disproportionately affected by the health consequences of lower socioeconomic status.
2. However even among groups with similar socioeconomic resources non-Māori have lower mortality rates than Māori. For example even among people in high income households there are substantial disparities in mortality rates between Māori and non-Māori (see figure over page).
3. Among both Māori and non-Māori populations, those with low income and no qualifications experience higher rates of mortality compared to high income groups and those with tertiary qualifications.
4. The different socioeconomic resources or positions of Māori and non-Māori ethnic groups account for at least half of the ethnic disparities in mortality for working-age adults and one-third for older adults.
5. During the 1980s and 1990s the socioeconomic resources of Māori, relative to non-Māori, worsened. This widening socioeconomic inequality explained about one-third to one-half of the widening gap in the mortality rates between Māori and non-Māori – at least for people of working age.

How did the researchers arrive at their conclusions?
The Decades of Disparity reports are based on the New Zealand Census-Mortality Study (NZCMS). This study anonymously and probabilistically links mortality data to census data, thereby creating the follow-up studies of the entire New Zealand census populations of 1981, 1986, 1991 and 1996 (and soon to be 2001). The NZCMS has two very important advances for research such as that published today in the third Decades of Disparity report. First, it overcomes problems of deaths for Māori (and Pacific people) being undercounted relative to census data. Second, the New Zealand census contains many measures of socioeconomic factors in addition to ethnicity, allowing mutual adjustment for both ethnicity and multiple socioeconomic factors.

The analyses for this third Decades of Disparity report involved first determining differences in death rates between Māori and non-Māori. Next, we examined death rates for Māori and non-Māori broken down by one socio-economic factor at a time. For example, we broke down both Māori and non-Māori populations into high, medium and low household income groups, and compared death rates. The figure over the page gives an example from the report. The higher up the point or line, the higher the death rate per 100,000 people. It is clear from this figure that no matter what level of income, Māori have higher death rates than non-Māori.

The more advanced analyses we undertook adjusted for multiple socio-economic factors at the same time, and allowed us to determine how much the relative gaps in death rates between Māori and non-Māori reduced as a consequence.

We are not aware of similar data sets of sufficient size in countries with similar histories of colonisation (e.g. Canada, Australia, USA) to allow similar analyses of mortality rates to those we have carried out in New Zealand.

Figure: Mortality rate trends from 1981–84 to 1996–99 for cross-classified groups of ethnicity, by income, cohort, sex and age group

ENDS

Source: Fawcett J, Blakely T, Robson B, Tobias M, Pakipaki N, Harris R. Decades of Disparity III: Overlapping Ethnic and Socioeconomic Mortality Inequalities in New Zealand, 1981–1999. Wellington: Ministry of Health, 2006.

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