Socioeconomic Status and Health

1
Socioeconomic Status and Health

• An overview of the evidencefor a
  connectionbetween wealth and health
• Ottawa, August, 2006

2
Sections

• Which indicators of health wealth to use?
• Individual evidence for link between SES and
  health
• Comparisons between societies
• Comparisons within societies (Britain, USA,
  Canada)
• Societal level income inequality and health

3
Health Indicators

• All-cause mortality
• Gives an overview non-specific doesnt weight
  by age
• Infant mortality
• Sensitive to socio-economic development to
  medical care
• PYLL
• Selects causes weights by age at death
• Morbidity indicators
• Usually partial coverage how available?
• QoL
• Captures non-fatal outcomes subjective (bias?)

4
Socioeconomic Indicators

• No ideal indicator. Some options
• Wealth
• Income readily measurable (in most societies),
  but only covers part of the picture doesnt
  apply well to elderly, to housewives, etc.
  Individual or family income? How to correct for
  family size?
• Occupation
• Reasonably comparable across countries may have
  direct relevance to health (exposures, hazards)
  difficult to classify score doesnt apply well
  to retired, housewives, children, etc.
• Education
• May be driving force behind occupation and
  income permanent unaffected by market
  fluctuations applies to those not in labour
  force established early in life so may not
  reflect subsequent changes
• Composite indicators
• Blend of above choice of weights for components
  is difficult.

5
1. Socioeconomic Status and Health

• (1a) Comparisons Between Societies

6
The Preston Curve (Preston SH. Population Studies
197529231-248)Note the non-linearity of the
relationship. This becomes crucial in
subsequent argumentsas we compare individual and
aggregate statistics
Data source World Bank Report, 1983
7
Sixteen years later have things changed? As
before, the health of the rich is not much
affected by changes in income, so transfers from
rich to poor would improve overall health.
Hence, poverty is important in poor countries
and the equity of income distribution is
important in richer countries.
Source 1998 World Bank Report
8

• (1b) Inequalities Within Societies
• Data from Britain, where most
• of the analyses began.
• Consider mortality in ages 15 64,
• i.e. adult, but premature mortality

9
Have things improved? Certainly!
Standardized mortality rates, England and Wales,
1841 to 1971
Males
Females
Source Townsend P, Davidson N. Inequalities in
health the Black Report. Penguin books, 1992
10
However there are major inequities. An early
example the Black Report
Age-Standardized Mortality Rates per 1,000 at
Ages 15 to 64 by Occupational Class, United
Kingdom, 1971
Source Townsend P, Davidson N. Inequalities in
health the Black Report. Penguin books, 1992
11
Life expectancy in England and Wales, by social
class, 1972-76 and 1992-96
Source Marmot M. Perspec Biol Med 2003 46
(Suppl 3) Table 1
12
The effect holds for both sexesSMR by
Occupational Class for Ages 15 to 64, England
Wales, 1970-72
13
And for many individual causes of death
Respiratory Deaths for Ages 15-64 by Occupational
Class,England Wales, 1970-72
14
And also among children All-cause SMRs (ages 0
14) by occupational class, England Wales,
1970-72
15
Most of the Effect Lies at Low Income Levels
Earnings and SMRs (UK, 1970)
SMR
1970 Earnings Pounds per Week
Source Wilkinson Class and Health,1986 pg. 110
16
Is it only premature mortality that shows a
social gradient?SMRs by occupational class and
age at death. England Wales, 1981-83
Occupationalclass
Age at death
Source Whitehead M. The Health Divide, table
11. Penguin books, 1992.
17
And disparities appear to be increasingTrends
in SMRs over Timein UK Men Aged 15 - 64
Unskilled
Partly Skilled Skilled Manual
Intermediate Professional
Source Wilkinson RG Class and Health. London,
Tavistock, 1986 Table 1.1
18
The effect occurs from birthPerinatal Death
Rates (up to day 7) by Occupational Class
England Wales, 1970-79
Class V
Class I
Source Wilkinson RG Class and Health. London,
Tavistock, 1986 Table 6.8
19
Postneonatal Death Rates (28 days-1yr.) by
Social Class England Wales, 1970-79
Class V
Class I
Source Wilkinson RG Class and Health. London,
Tavistock, 1986 Table 6.7
20
Whitehall 2 Cohort Study Mortality Trends over
Time in Men Initially Aged 40-64
Cumulative Probability of death (per cent)
Other
Clerical
Professional Executive
Administrative
Year of follow-up
Source Marmot et al. Lancet 19913371387-1393
21
Potential Years of Life Lost (All Causes) England
Wales, 1971 1991Message there are two-fold
differences in mortality rates across
occupational groups. The deficit occurs mainly
from the lowest class. While overall mortality
rates have fallen over the 20 years, the
inequality has remained.
Occupational Class V IV III II I
22
Potential Years of Life Lost (Accidents
Violence). England Wales, 1971 - 1991
Social Class V IV III II I
23

• The Black Report was published in 1980 and,
  despite government attempts to hide it, produced
  significant reactions
• For example, the British Health Education Council
  published The Health Divide in 1988. It focused
  on inequities (inequalities perceived as being
  unfair)
• Other countries in Europe began to investigate
  whether they, too, experienced health
  disparities. Many countries reported to the WHO
  that health disparities increased during the
  1980s.
• This shifted health disparities up the political
  agenda
• Marmot (2003) The point I wish to draw out of
  these figures is that if the life expectancy gap
  can increase, it can, in principle, decrease. If
  we think this is a problem worth tackling, the
  challenge is to understand the reasons for the
  social gradient in order to do something about
  it.

24
(ii) Data from Canada, where Statistics Canada
began to take notice in the 1990s
25
Crude and age- standardized mortality rates,
Canada, 1920-2000
Deaths per 1000 population
26
Age-standardized mortality rates from
cardiovascular disease, Canada, 1951-1995
Deaths per 100,000 population
27
Deaths avoided due to declining death rates in
Canada Numbers of deaths that would have
occurred in 1989 if 1971 rates had applied.
Age Males Females Total lt 1
2,336 1,680 4,016 1 - 14 896
599 1,495 15 - 34 1,373 822
2,195 35 - 54 5,547 2,597 8,144 55 -
74 12,265 7,238 19,503 75 5,707
12,037 17,744 Totals 28,124
24,973 53,097
28
Life expectancy at birth by age and sex, Canada,
1921-2000
Life expectancy (years)
29
So, what about Social Class?Life Expectancy at
Birth, Canada, 1971 and 1986
Years
Females, 1986 Females, 1971 Males,
1986 Males, 1971
(High) Income Quintiles
(Low)
30
Life expectancy at birth, by income quintile,
urban Canada, 1971 1986

• Income classified by proportion of census tract
  falling below Stats Canada low income threshold
• Quintiles within each CMA
• Apparently, gradient leveled somewhat by 1986
• Wilkins et al. Health Reports 19881137

High Low
31
Cumulative fetal and infant mortality by weeks
since beginning of pregnancy, by maternal
education, Québec, 1990-91
Per 1000 total births
Weeks since beginning of pregnancy
32
Infant Mortality by quintiles of wealth, Canada
1971 - 1996
per 1,000
Source Russ Wilkins, Socioeconomic inequality
in health outcomes.Statistics Canada, 2003
33
Potentially Modifiable Mortality

• Potential years of life lost, Canada 1986, prior
  to age 75
• Includes infant deaths
• For each cause they subtracted rates in quintile
  1 from other quintiles. The result is expressed
  as a percentage how much improvement would occur
  if everyone had the rate in the highest income
  quintile?

34
Diminishing Disparities in Infant Mortality,
Canada 1971 - 1996

• Poor-Rich Total-Rich Excess
• Year RD RR RD RR Deaths
• 1971 9.8 1.97 4.8 1.47 2028
• 1986 4.8 1.82 1.7 1.29 666
• 1991 2.9 1.64 1.3 1.29 577
• 1996 2.6 1.67 1.3 1.33 513

RD difference in infant mortality rates between
rich and poor RR ratio of mortality rates,
poor rich Excess deaths number of deaths
that would have been avoided had death rates for
rich applied to all deaths
Source Russ Wilkins, Socioeconomic inequality
in health outcomes, 2003
35
Low Income and Low Birth Weight Ottawa Area, 1991
Rates of Low Birth Weight, 1990-92
Vanier
Ottawa
Gloucester
Nepean
Kanata
Percentage of Families Below Low Income Cutoff
(Ross Wolfson, Statistics Canada)
36
Why is birth weight important? The Barker
hypothesis. Death rates from IHD by birth weight
(n 15,726)
Death Rate
Birthweight (kg)
Source Barker DJP et al. Weight in infancy and
death from ischaemic heart disease. Lancet
1989I577-580
37
Examples of associations between SES indicators
Income and School Achievement Eastern Ontario,
1996-97
of children scoring below Ontario standards
Vanier
Cornwall
Kingston
Gloucester
Ottawa
Kanata
Percentage of Families Below Low Income Cutoff
(Educational Quality Assurance Office of Ontario)
38
(iii) U.S.A.
39
The effect of income is much greater among poor
people. Data from U.S. National Longitudinal
Mortality Survey (1980-1990)(graph based on a
logit model of the data)
10-year age-adjusted probability of dying
Family Income in 1980
Source Deaton A. Health, inequality and
economic development www2.cid.harvard.edu/cidmh/w
g1_paper3.pdf
40
And race has a greater effect among the
poorLife Expectancy at age 45 by Family Income,
Race and Sex. United States, averaged over
1979-89
White Females
Black Females
White Males
Black Males
Life Expectancy at age 45
lt10,000 10,000- 15,000-
25,000 14,999
24,999 Family Income
Source GA Kaplan et al. In Promoting Health
Intervention Strategies from Social and
Behavioral Research. Institute of Medicine,
2000, page 40
41
Low Birth weight, by Education and Race /
Ethnicity, United States, 1996
Years of Education
Low Birthweight per 1,000 Live Births
White Black Hispanic Native
Asian
Source GA Kaplan et al. In Promoting Health
Intervention Strategies from Social and
Behavioral Research. Institute of Medicine,
2000, page 44
42
Mortality by Family Income, MRFIT
lt7.5
10
15
20
25
30
Annual family income in thousands of US dollars
43
2. Income Inequality and Health

• As countries become wealthier and move through
  the epidemiologic transition, the leading cause
  of differences in mortality changes from material
  deprivation to social disadvantage.
• Inequality hypothesis proposed in late 1970s
  Rodgers, Flegg and others. In industrial
  countries, mortality rises with range of incomes
  (Gini coefficient) in the society.
• The Wilkinson Hypothesis (1990s) for defined
  geographical areas, mortality rises with the
  level of disparity in incomes.
• Corollary occupation and education gradients in
  health do not occur in societies with low income
  disparities.
• Material deprivation provokes poverty and
  infectious disease social disadvantage provokes
  stress and chronic disease.
• (2 a) Comparisons Across Countries

44
Life Expectancy and Income Inequality, 1970
Life expectancy (M F combined)
Sweden
r -0.81
Norway
NL
Japan
Canada
France
UK
Australia
Spain
USA
W.Germany
More equal
Less equal
Gini coefficients of inequality of distribution
of income, standardized for household size
Adapted from Wilkinson R. Unhealthy societies
the afflictions of inequality. London, Routledge,
1996, p 84.
45
Income Inequality and Life Expectancy, 1981
Sweden
Switzerland
NL
Norway
Australia
Canada
USA
UK
W. Germany
r 0.86
46
Social Class Differences in IMR in England
Wales, Compared to Sweden
England Wales
Sweden
Occupational class
Note Income inequality is substantially higher
in Britain than in Sweden
Source R. Wilkinson. Unhealthy societies the
afflictions of inequality. Routledge, 1996
47
Changes in the Dispersion of Income, 1980 - 1991
United Kingdom
United States
Canada
Australia
Japan
Austria France
Denmark, Sweden
Germany Norway
Note the chart shows the ratio of the earnings
of someone at the 90th centile of income to the
earnings of someone at the 10th centile,
artificially set at 1 for 1980. Source OECD
48
Some difficulties in nation-level studies

• Lack of good quality international data,
  collected in consistent manner in different
  countries. E.g., in some studies Sweden is rated
  very egalitarian, in others less so than Britain!
• Results seem to vary according to era from which
  data taken
• Failures to replicate. Mellor Milyo found that
  controlling for education removes effect (for
  infant mortality). Judge et al found correlation
  of -0.17 (n.s.)
• General conclusion income inequality does not
  appear to drive overall mortality in industrial
  countries may do so for infant mortality.

49
2 (b) Comparisons Within Countries

• These appear to avoid some of the difficulties in
  cross-national comparisons data are usually
  collected by a single agency (e.g., Statistics
  Canada)
• Income data usually collected via the census
  (rather than surveys). Correlation usually
  found lots of replications. Usually around 0.7
  (i.e. explains half of the difference between
  areas).
• Wagstaff The first point to emerge from these
  studies is that they all confirm that income
  inequality is strongly associated with mortality,
  even after controlling for the average level of
  community income. (Annu Rev Public Health
  200021554)

50
Illustration of Within-Country Results
Inequality and the log-odds of mortality. U.S.,
1990
Source Deaton A. Health, inequality and
economic development http//www.cmhealth.org/doc
s/wg1_paper3.pdf
51
Questions Concerns

• Data are pooled across ethnic (etc) groups
  presumably income inequality is a proxy for
  various other factors. As you focus down onto
  selected groups the association (not
  surprisingly?) is reduced. So, if the effect
  comes from inequality between groups (e.g.,
  blacks whites in the US), is this merely a
  proxy for race, and does income inequality have
  no direct effect?
• There is an issue of scale what inequality
  should we use when analysing individual data
  (country level, state level, community or
  neighbourhood level?) What is the persons
  reference point?
• Individual-level analyses generally show very
  modest inequality effects (RR 1.2, etc)
• General conclusion is that health is an
  increasing, nonlinear function of absolute income
• So, there may be no direct effect of income
  inequality at all, but race, geography, social
  support services, or ?

52
Categories of Explanation (EPI 6181 topic 2)

• Theories that explain the pattern of
  relationships between SES and health cf. the
  economic literature (e.g., Wagstaff, below).
  What form does it take?
• Theories of mechanisms for the link e.g.,
  lifestyles, genetics, access to care. How does
  it work?
• Theories on determinants of the relationship
  the field of population health. Why does it
  arise?

53
The concave income-health relationship explanation
The blue line shows the familiar concave
relationship of income and health Consider two
people A and B. Mean income µ. Their aggregate
health is represented by the green line this is
extended to the ordinate. Redistribute 1000
from A to B (dotted arrows),reducing income
inequity. µ stays the same. Overall average
health now shown by red line. Redistributing
income has caused overall healthto rise, because
the damage to As health is less (because the
blue curve is flatter)than the improvement to
Bs.
Health
Income
µ
B B1000
A-1000 A
See, e.g., Wagstaff and van Doorslaer. Annual
Review of Public Health 2000 21 543.
54
The Debate over Relative or Absolute Income

• It is logical that there is a minimum income
  required for basic amenities (food and shelter).
  In very poor places, this is the limiting factor
  in health.
• But in richer places most people are above the
  poverty line, does improvement in health reflect
  increase in absolute wealth, or is it driven by
  something else, such as relative wealth? (and if
  so, how and why?)
• Marmot, 2003 The GNP in Costa Rica is about
  2,000 per person life expectancy for men is 74
  years. Among black men in the U.S., mean income
  is around 26,000 and life expectancy is 66.
  Adjusting for different buying power brings the
  Costa Rica figure to about 6,000 per person,
  still one-quarter of the US figure, and yet they
  live 8 years longer.

55
(continued)

• A consistent finding is that within countries or
  states, individual health is related to
  individual income, but comparing between states
  average health is independent of average income,
  but is negatively related to income inequality.
  I.e., it depends on which comparison you are
  making (within or across places)
• Wilkinson argued (for richer countries)
  Mortality is associated with relative income.
  Someone with an absolute income that equals half
  of the US average might do better to be
  moderately well off in Greece or Spain than poor
  in the US (BMJ 1998 316 1611) and health is
  powerfully affected by social position
• Relative inequality in income may correspond to
  absolute discrimination and social exclusion.
  (Marmot, Perspec Biol Med 200346 (suppl 3)S17).

56
Wagstaff van Doorslaers hypotheses

• Economic perspective what is the main driver in
  the relationship
• Absolute income?
• Relative income?
• Deprivation?
• Relative position?
• Income inequality?
• Conclusion it depends very much whether you are
  explaining individual health, or community, or
  population health patterns
• Annual Review of Public Health 200021543

57
Poverty may explain the link between income
inequality and health
Two populations, equal in mean income, but
different in levels of income inequality
Population A
Population B
Mean income
Poverty line
Population B shows a much wider spread of
incomes high income inequality. Substantial
numbers of people fall below the poverty line
andaccordingly their health suffers, pulling the
average health statistics downward
Population A shows a narrow spread of
incomeslittle income inequality.No-one falls
below the poverty lineand health is reasonably
good
58
Deatons presentation of relative income.
Imagine two groups with different average income
(the purple group is further to the right).
Within each group health rises with income
(solid sloping lines). But they have equal
average health (the ellipses are the same
vertical height). However, when you combine the
two groups, you increase income inequality but
the association between health and income is
reduced (dotted line). Hence, within each group,
relative income is more important than absolute
income, but on combining groups income inequality
becomes more significant.
Health
Group 1
Group 2
Income
Low
Source Deaton A. Health, inequality economic
development www2.cid.harvard.edu/cidmh/wg1_paper3.
pdf
59
The processes are complex and may change over
time. The wealth of a mother may affect the
health of her child, and from the previous
slides, it may very well be relative income that
counts. But the following diagram makes the
point that a mothers income relative to the
average income varies according to her age.
Young mothers are (on average) poorer than older
ones and the disparities have grown over time.

Age at delivery
Aboveaverageincome
Belowaverage
Source C. Lochhead. ISUMA 2000141-44.
(www.isuma.net/v01n02/index.htm)
60
Is it the indicator of Class?

• Goldblatt (1990) compared professional men living
  in their own home and who had access to a car
  (SMR 67) to all men who lacked access to a car
  and lived in rented accommodation (SMR 123).
  This gradient is similar to that based on the
  occupational classification, so maybe the
  occupational approach is not bad.
• Other studies (Carstairs Townsend) used
  area-based indicators of social and material
  deprivation. They found consistent relationships
  with a range of health indicators again, it may
  not make much difference which indicators of
  class you use.

61
Here an index of deprivation is based on nine
variables, which should compensate for
inadequacies in any one of them. Life Expectancy
at Birth, by decile of deprivation gender. New
Zealand, 1995-97
Life Expectancy, in years
Deprivation decile (composite score of nine
variables)
Source Social inequalities in Health New
Zealand 1999. N.Z. Ministry of Health
62
Do conventional risk factors account for link
between SES and mortality? Prevalence of Regular
Smoking, by deprivation decile gender (ages
45-64) New Zealand, 1996
regular smokers
Deprivation decile (composite score of nine
variables)
Source Social Inequalities in Health New
Zealand 1999. N.Z. Ministry of Health
63
Prevalence of obesity among women, by SES and by
SES of parents. U.S. data.
Prevalence
(N in each group ranges from 291 to 362)
Socioeconomic status
Note lower SES women are more often obese than
their parents higher SES slightly less obese
the disparities appear to be increasing.
Source Goldblatt PB et al. Social factors in
obesity. JAMA 19651921039-1044.
64
Prevalence of high blood pressure, high
cholesterol and obesity, Canada, 1986-92, by
educational level
Percentage
Years of Education
Source Federal Task force on Population Health,
1996
65
Prevalence of Activity Limitation (ages 15),
Canada, 1991
Percentage
(High) Income Quintiles
(Low)
Statistics Canada. Report of 1991GSS.
66
The previous slides suggest that SES affects risk
factors.So, lets adjust for conventional risk
factors and see if the SES Health link remains,
or if it was due to the SES distribution of risk
factors. Data from Whitehall I Cohort Ten-Year
Relative Risks of Death (all causes)   (a)
unadjusted, and (b) adjusting for CVD risk factors
Relative risk
Relative risk
(b) Adjusted for smoking, BP cholesterol
(a) Raw data
Civil service occupational categories Other
Clerical Professional
67
Relative Risk of Death from CVD by Occupational
Grade, Showing Differences that can be Explained
by Conventional Risk Factors. Whitehall I
Study.Message most of the variation (black
bars) is not attributable to common risk factors.
So, what does SES, or class represent??
RR
Unexplained
Other B.P. Smoking Cholesterol
68
Could it be access to good quality medical care?
MaybeTrends in age-standardized mortality from
causes that are, and are not, amenable to
medical treatment
Deaths unrelated to quality of care
Hungary, Czech,Poland
Canada, U.S.
Germany, U.K.
Hungary, Czech,Poland
Deaths amenable to care
Germany, U.K.
Canada, U.S.
Source Boys RJ et al. Br Med J 1991303879-883.
The contribution of medical care is to treat
illness when it occurs, not to prevent its
occurrence M. Marmot.
69
Complications! Interaction between occupational
class and country of origin for immigrants to
Britain. Black Report
Age-Standardized Mortality Rates per 1,000 at
Ages 15 to 64 by Occupational Class and Country
of Immigration, United Kingdom, 1971
This is bizarre!! Why the reverse trend for
immigrants?
70
Some conclusions

• Poverty is clearly linked to health
• Income inequality is a useful marker of risk, but
  represents the likely occurrence of other factors
  that adversely affect health
• Depends on level of investigation of the
  phenomenon individual vs. community-level vs.
  population health
• Interactions are likely. Sen (Development and
  Freedom, 1999) relief from any one of several
  interlinked deprivations helps to promote relief
  from the others
• This course will try to identify the inter-linked
  deprivations that affect health
• Will review theories of 3 types What?, How? and
  Why?