Research Update
Death and tax brackets: link between income inequality and mortality holds true in US, but not in Canada
CMAJ 2000;162(13):1866
The income gap between the haves and have-nots is not strongly linked to death rates in Canada, unlike in the US, according to recently published international research (BMJ 2000;320:898-902).
When Michael Wolfson and colleagues compared income inequality and all-cause mortality at the state or provincial and at the metropolitan level, they found no association in Canada. There was a strong relation, on the other hand, in the US data — confirming results from previous studies.
The research team defined income inequality as the proportion of total family income received by the less well-off 50% of households. Mortality data were grouped and adjusted by age. Wolfson's study compared 50 US states and 10 provinces, as well as 282 US and 53 Canadian metropolitan areas.
"We were quite surprised by the findings," said Michael Wolfson, director general of the analysis and development branch at Statistics Canada. "We had hypothesized that we would find the same association here as in the United States, just not as steep a slope."
Although the team's findings show that the strong association between income inequality and mortality in the US is absent here, Wolfson is quick to point out that the research provides no evidence why this is so. Possible explanations include the more equitable distribution of wealth and the greater heterogeneity of communities in Canada, says Wolfson. "There appears to be something going on in Canada that has allowed us to grow more 'sharing' cities, which seem to have quite positive health effects." While Canada's health care system likely plays a significant role in dampening the effects of income disparity, Wolfson believes it is not the sole reason for the marked difference between the 2 countries.
In looking at the combined figures for North America, the researchers estimate that if the relationship between income disparity and mortality were causal, a 1% increase in the share of total income for the bottom half of households would prevent 21 deaths per 100 000 population. — Greg Basky, Saskatoon
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