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Nancy A Ross a Statistics Canada, Ottawa, ON, Canada K1A 0T6, b Centre for Health Services
and Policy Research, Department of Health Care and Epidemiology,
University of British Columbia, Vancouver, BC, Canada V6T 1Z3, c School of
Public Health, University of Michigan, Ann Arbor, MI 48109-2029, USA
Correspondence to: N Ross rossnan{at}statcan.ca
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Abstract |
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Objective:
To compare the relation between mortality and income inequality in Canada with that in the United States.
A large body of research reports an association between income
distribution and health1-14 and a range of
hypotheses articulates possible mechanisms operating between income
inequality and poor health outcomes.
15 16
Among American
states, mortality is more weakly correlated with mean or median state
income than it is with various measures of how that income is shared
within a state.
5 6
US metropolitan areas with greater
income inequality also have significantly higher mortality than
metropolitan areas with more equal income distributions, independent of
the median income of the metropolitan area.8
Collectively these studies point to the conclusion that populations in
areas where there is an unequal income distribution have higher
mortality than populations in more homogeneous areas. While some have
claimed that the relation between income inequality and mortality is an
artefact of the non-linear relation between income and mortality at the
individual level,17 Wolfson and colleagues18
and others reporting findings from multilevel
analyses19-22 provide substantial evidence for a
non-artefactual explanation.
We compared income inequality and age grouped mortality in Canada and
the United States. We considered two levels of geographic aggregation:
state/provincial and metropolitan area. The comparison of
states/provinces and US metropolitan areas is compelling in that it has
the potential to highlight characteristics and policies specific to
particular social contexts that could affect health. While the product
of similar economic, social, and cultural forces,23 Canada
and the United States also have some major differences, especially with
regard to social policy and racial divisions. US metropolitan areas
differ greatly from Canadian metropolitan areas in terms of the degree
of economic and social inequality they generate and the ways in which
unequal material circumstances and social relations are
institutionalised through policy and urban political
structure.
24 25
While economic segregation and social
polarisation are less pronounced in Canadian cities, some studies have
suggested that they increased in the last decade of the 20th
century.
26 27
Incomes at the bottom of the distribution are higher in Canada than in
the United States, and while inequality in net income rose between 1985 and 1995 in the United States it actually fell slightly in Canada
because of the redistributive effects of Canadian taxation and transfer
policies.28 Furthermore, since the 1980s, pay inequality
in Canada has widened much less than in the United States.
28 29
In the United States, labour market
prospects for low skilled workers have been poor over the past two
decades. Hypotheses such as the growing skill requirements of a global economy, deindustrialisation, relocations of employers to suburban areas, and racial discrimination have been offered to explain these
trends.30
Associations between income inequality and mortality were studied
in the 50 US states and the 10 Canadian provinces, as well as in 282 US
and 53 Canadian metropolitan areas with populations greater than
50 000 (as of 1990 in the United States and 1991 in Canada). All
mortalities were age standardised to the Canadian population in 1991. The associations were examined separately by the following age and sex
groupings for the states and provinces: infants (less than 1 year),
children and youth (1 to 24 years), working age men (25 to 64 years),
working age women (25 to 64 years), elderly men (65 years and older),
and elderly women (65 years and older). Age groupings were the same for
metropolitan areas but breakdowns by sex were unavailable.
Inequality was operationalised as the proportion of total
household income accruing to the less well off 50% of households within an area (that is, the "median share" of income). In a
setting of perfect equality, the bottom half of the income distribution receives 50% of the total income and the area then has a median share
value of 0.50. The indicator has recently been used in similar studies
on inequality and mortality,
5 8
and thus allowed for
comparability of results. Moreover, tests with a range of other
measures of inequality and polarisation suggested that this choice did
not substantially affect the results.
US data
Canadian data
Model building and general linear testing
States and provinces
Design:
The degree of income inequality, defined as the percentage of total household income received by the less well off
50% of households, was calculated and these measures were examined in
relation to all cause mortality, grouped by and adjusted for age.
Setting:
The 10 Canadian provinces, the 50 US states, and 53 Canadian and 282 US metropolitan areas.
Results:
Canadian provinces and metropolitan areas generally had both lower income inequality and lower mortality than US
states and metropolitan areas. In age grouped regression models that
combined Canadian and US metropolitan areas, income inequality was a
significant explanatory variable for all age groupings except for
elderly people. The effect was largest for working age populations, in
which a hypothetical 1% increase in the share of income to the poorer
half of households would reduce mortality by 21 deaths per 100 000.
Within Canada, however, income inequality was not significantly
associated with mortality.
Conclusions:
Canada seems to counter the increasingly
noted association at the societal level between income inequality and mortality. The lack of a significant association between income inequality and mortality in Canada may indicate that the effects of
income inequality on health are not automatic and may be blunted by the
different ways in which social and economic resources are distributed
in Canada and in the United States.
![]()
Introduction
Top
Abstract
Introduction
Methods
Results
Discussion
References
![]()
Methods
Top
Abstract
Introduction
Methods
Results
Discussion
References
Mortality data for the 50 US states came from the Centers for
Disease Control (CDC) Wonder website. Mortalities by state, sex, and
age were averaged over three years (1989-91) to improve the stability
of the estimates. State median share proportions and the median income
values were generated from the 1990 US census and have appeared in a
previous paper by Kaplan and colleagues.5
Metropolitan area mortalities and median share proportions were
from the work of Lynch and colleagues.8
The income inequality data for Canada came from a micro data file
of the 1991 census of Canada. The income definition used in the
Canadian calculations, like that for the United States, included income
from wages and salaries, net income from self employment, government
transfers, and investment income. Canadian mortality data were based on
three year averages (1990-2) by province, sex and age group, and by
metropolitan area and age group.
Multiple regression analyses were conducted only on the
metropolitan area data because of the small number of Canadian
provinces. Given that the reliability of the estimated mortality is
related to the populations of metropolitan areas we used weighted
regression with population size as the weight. Use of these weights
ensures that the regression line goes through the mean mortality of the
entire population under study. Furthermore, the use of such a weighted
regression allows for the unobserved differences in mortality between
Canada and the United States, potentially because of differences in
social structure, to be taken into account through the use of a dummy
variable.31
![]()
Results
Top
Abstract
Introduction
Methods
Results
Discussion
References
The median share values ranged from 0.17 (least equal) in
Louisiana to 0.23 (most equal) in New Hampshire for the US states,
while the range for the Canadian provinces was 0.22 (least equal) for
Saskatchewan to 0.24 (most equal) for Prince Edward Island. The median
proportion of income received by the less well off half was 0.21 for US
states, while for Canadian provinces it was 0.23. There was little
overlap between US states and Canadian provinces in regard to income
inequality with only Wisconsin, Vermont, Utah, and New Hampshire
sharing similar income distributions to the Canadian provinces.
0.62), working
age men (r=
0.81), working age women
(r=
0.81), elderly men (r=
0.44), elderly
women (r=
0.42), and all age (r=
0.68)
mortality in combined US states and Canadian provinces calculations.
Figure 1 shows a weighted linear fit (the areas of the circles are
proportional to the population size) between income inequality and
mortality for working age men at the state/provincial levels. The
strongest relation with inequality was for working age populations. The
Canadian provinces seem almost like a more equitable extension of the
US data, by having lower mortality and lower inequality. Within Canada,
however, the slope of the weighted regression line was in the expected direction but was not significantly different from
zero.

View larger version (20K):
[in a new window]
Fig 1.
Mortality in working age men by proportion of
income belonging to the less well off half of households, US states
(1990) and Canadian provinces (1991). Mortality standardised to
Canadian population in 1991. State abbreviations: LA-Louisiana;
MS-Mississippi; AL-Alabama; SC-South Carolina; FL-Florida; TX-Texas;
CA-California; AR-Arkansas; NH-New Hampshire; MN-Minnesota. Province
abbreviations: QC-Quebec; NS-Nova Scotia; NB-New Brunswick;
ND-Newfoundland; PE-Prince Edward Island; ON-Ontario; AB-Alberta;
BC-British Columbia; MB-Manitoba; SK-Saskatchewan
Metropolitan areas
The populations of the 282 metropolitan areas in the United States
ranged from 56 735 (Enid, Oklahoma) to 18 087 251 (New York city)
with a median size of 242 847. The populations of the 53 metropolitan
areas in Canada ranged from 50 193 (Saint-Hyacinthe, Quebec) to
3 893 046 (Toronto, Ontario) with a median size of 116 100. The
median share values ranged from 0.15 (least equal) in Bryan, Texas, to
0.25 (most equal) in Jacksonville, North Carolina, for the United
States while the range in Canada was 0.22 (least equal) for Montreal,
Quebec, to 0.26 (most equal) for Barrie, Ontario. The median proportion
of income received by the less well off half of households for US
metropolitan areas was 0.21 while for the Canadian metropolitan areas
it was 0.23.
0.37), children and youth (r=
0.38), the working age population
(r=
0.55), the elderly population (r=
0.25),
and all ages combined (r=
0.43) for the pooled 335 metropolitan areas in the United States and Canada. Within Canada, however, there was no statistical relation between inequality and
mortality at the metropolitan area level as evidenced by the weighted
linear fit (dashed line) to the Canadian data points for working age
mortality in figure 2.
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Discussion |
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Our analysis of data from Canada and the United States has shown that variations in the equality of the income distribution are associated with mortality. The relation was strongest for working age populations but was much weaker in elderly populations. Other research has suggested that differential working age mortality across populations may be a more powerful measure of relative disadvantage than the traditionally studied infant mortality differential. 20 34 35 As for the attenuation seen in elderly populations, current household income may not be a useful measure for this group given that income levels before retirement or measures of wealth better reflect their social position.36
There were no significant asociations between income inequality and mortality in Canada at either the provincial or metropolitan area levels, whereas such associations were apparent in the United States. The absence of an effect within Canada may indicate that the relation between income inequality and mortality is non-linear (that is, at higher levels of equality there is a diminishing effect on health) or that the relation between income inequality and mortality is not universal but instead depends on social and political characteristics specific to place. The first explanation suggests that reducing income inequality would be beneficial for population health. The latter explanation suggests that specific policies can be implemented to buffer the health effects of income inequality.15
The juxtaposition of Canadian and US policies in these analyses raises questions about differences in the social and material conditions of the two countries that mute (in Canada) and exaggerate (in the United States) the relation of inequality to mortality. One plausible difference is the greater degree of economic segregation in large US cities.20 Such segregation can create a spatial mismatch between workers and jobs and large inequalities in provision of public goods and services (for example, schools, transportation, health care, policing, housing, etc) because of concentrations of people with high social needs in municipalities with low tax bases.37 The population health effects of inequalities in provision of these public goods and others like parks, libraries, and recreation facilities need to be the focus of future research. 15 38
Another major difference between the two countries is the way in which resources such as health care and high quality education are distributed. In the United States these resources tend to be distributed by the marketplace so their utilisation tends to be associated with ability to pay; in Canada they are publicly funded and universally available. As a consequence, in the United States an individual's income, in both a relative and absolute sense, is a much stronger determinant of life chances and, in turn, "health chances" than in Canada.
These comments underscore the point that observations of contexts in which income inequality has health consequences and those in which it does not provide opportunities to examine the role of variations in economic and social policy which structure the availability of resources and demands placed on individuals. Collectively, these resources and demands modify the day to day experiences of individuals thereby creating different patterns of health and disease in different places.
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What is already known on this topic
Income inequality has been shown to be associated with mortality when countries, US states, and US metropolitan areas have been compared What this study addsData from Canada have been added to the research on the relation between income inequality and mortality, thus providing a more complete picture for North America Income inequality is strongly associated with mortality in the United States and in North America as a whole, but there is no relation within Canada at either the province or metropolitan area level Overall, the comparison between Canada and the United States suggests that policies directed toward evening out the income distribution may reduce the effects of inequality on health |
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Acknowledgments |
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Contributors: NAR performed the analyses and wrote most of the paper. MCW had the original idea for the research and helped to write the paper. JRD developed some of the conceptual arguments around the differences between Canada and the United States and participated in the writing of the paper. J-MB provided statistical expertise and helped to write the paper. GAK and JWL inspired the analysis and participated in the design and writing of the final version of the paper. NAR and MCW are guarantors.
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Footnotes |
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Funding: Statistics Canada, Canadian Population Health Initiative, Social Sciences and Humanities Research Council of Canada (postdoctoral fellowship No 756-98-0194), University of Michigan Initiative on Inequalities in Health.
Competing interests: None declared.
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(Accepted 20 January 2000)
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