Annals of Epidemiology 26 (2016) 238e240
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Annals of Epidemiology
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From the American College of Epidemiology
Social inequalities in health: a proper concern of epidemiology
Michael Marmot FRCP *, Ruth Bell PhD
Institute of Health Equity, Department of Epidemiology and Public Health, UCL, London, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 24 February 2016
Accepted 24 February 2016
Available online 3 March 2016
Social inequalities are a proper concern of epidemiology. Epidemiological thinking and modes of analysis
are central, but epidemiological research is one among many areas of study that provide the evidence for
understanding the causes of social inequalities in health and what can be done to reduce them.
Understanding the causes of health inequalities requires insights from social, behavioral and biological
sciences, and a chain of reasoning that examines how the accumulation of positive and negative
influences over the life course leads to health inequalities in adult life. Evidence that the social gradient
in health can be reduced should make us optimistic that reducing health inequalities is a realistic goal for
all societies.
Ó 2016 Elsevier Inc. All rights reserved.
Keywords:
Social inequalities in health
Epidemiology
Social determinants of health
We doubt that any would question whether social inequalities in
health are a proper concern of public health. If a concern of public
health then they are a proper concern of epidemiology given its
focus on the causes of the distribution of health and disease in
populations. Understanding the causes of social inequalities in
health requires looking beyond the immediate causes of ill-health,
such as smoking or infections, to the determinants of the social
distribution of these causesdwhat we have termed the “causes of
the causes.”
Recently, one of us published The Health Gap, which reviews
global evidence on health inequalities and points to what can be
done to reduce them. We would not like to count how many of the
references in The Health Gap [1] are to epidemiological articles.
Some are. But, The Health Gap also cites social psychology, developmental psychology, political economy, econometrics, welfare
economics, sociology, behavioral genetics, biology, philosophy, and
a variety of UN agencies; not to mention accounts of police officers,
fire fighters, and community activists.
There is no question that the way of thinking behind understanding the causes of the causes of health inequalitiesdpopulation
thinkingdis epidemiological. But, the methods used to address the
problem of health inequalities are much more varied. In contrast to
some, we do not take the view point of a hierarchy of methods from
case-control studies, through longitudinal studies to randomized
control trials (RCTs). Almost none of the evidence for the
interventions proposed in The Health Gap and in previous reviews of
* Corresponding author. Institute of Health Equity, Department of Epidemiology
and Public Health, UCL, London, UK. Tel.: þ44 207 679 1705.
E-mail address: [email protected] (M. Marmot).
http://dx.doi.org/10.1016/j.annepidem.2016.02.003
1047-2797/Ó 2016 Elsevier Inc. All rights reserved.
the evidence [2e4] come from RCTs. Nor could it be so in the
foreseeable future. Evidence-based policies and practice are vital;
but the types of evidence that we touch on below do not lend
themselves to a suite of RCTs. That said, Banerjee and Duflo have
emphasized the possibility of RCTs in economics [5]. A good
development. But RCTs won’t solve the problem of health
inequalities.
The challenges both for research and policy are the social
gradient in health, accumulation of advantage and disadvantage
through the life course, and the importance of orienting a country’s
approach to development beyond a narrow focus on economics to
one that emphasizes human flourishing.
Challenge of the gradient: more than poverty
The distribution of health within countries follows a social
gradient: people lower in the social hierarchy have lower life
expectancy and higher risk of illness than those higher-up in the
social hierarchy. The nature of social stratification varies in form
and magnitude across countries but includes dimensions such as
income, wealth, education, occupation, gender, ethnicity, and area
of residence. The social gradient means that not only the poorest
but the majority have worse health and shorter lives than the best
off in society. There must be a concern for poverty, of course, but
also for social inequalities across society.
The steepness of the social gradient in health varies across
countries and over time. Although social stratification may be an
inevitable feature of societies, the fact that the slope of the health
gradient is not fixed provides grounds for optimism and suggests
two strategies for reduction in health inequalities. First, address the
M. Marmot, R. Bell / Annals of Epidemiology 26 (2016) 238e240
239
form and magnitude of social stratification by tackling gross
inequalities in the distribution of power, money, and resources.
Second, improve the conditions in which people are born, grow,
live, work, and age, so position in the social hierarchy matters less
for health [2].
Accumulation of advantage and disadvantage through the life
course
In epidemiology, rightly, we try to sort out which of a set of
correlated variables is the key one related to ill-health. Much of the
debate over diet, for example, arises because people do not eat
nutrients, or even single foods; they have patterns of food intake.
More of one thing commonly means less of another. This problem is
even more acute when we look at social determinants of health.
Low social position is related to many disadvantages, each of which
may be playing a role in leading to health disadvantage. By way of
illustration, in The Health Gap, readers meet two young men from
Baltimore, MD. One, LeShawn, is from the Upton/Druid Heights
neighborhood, a poor inner region of the city where half of all
families are single parent families, median income is low at $US
17,000, 40% of children lack reading proficiency at age 10 years, over
half of pupils miss at least 20 days of high school a year, and 90% do
not go on to college. Each year, a third of boys aged 10e17 years are
arrested for some kind of juvenile disorder, there are around 100
nonfatal shootings each year and nearly 40 homicides per 10,000
residents. Male life expectancy at birth is 63 years. The accumulation of disadvantage that faces LeShawn and other young people
growing up in the Upton/Druid Heights neighborhood has implications for crime, for civil unrestdsuch as that which arose in
2015dand for health. Contrast LeShawn’s life chances with those of
Bobby growing up in Roland Park, an affluent neighborhood of
Baltimore where 93% of families are two parent families, median
income is $US 90,000, 97% of pupils achieve “proficient or
advanced” in third-grade reading, only 8% missed 20 or more days a
year of high school, 75% complete college, juvenile arrests stand at
one in fifty each year, there were no nonfatal shootings in
2005e2009 and four homicides per 10,000. In Roland Parkmale, life
expectancy at birth is 83 years, 20 years higher than in the poor
inner city area.
Low education, low income, deprived neighborhoods all may be
playing a role in causing health inequalities. Problems in early
childhood may cast a long shadow over all these.
Fig. 1. Socioeconomic position and cognition. Q ¼ cognitive score. Feinstein (2003) [6].
Similarly, chains of reasoning, backed up by different kinds of
evidence, link experiences in early childhood with health in adult
lifedthe life course approach. Using longitudinal studies that track
a cohort over time, epidemiology can help to inform this life course
approach to understanding the causes of health inequalities. A good
level of development in the early years of life lays the foundation for
future life chances and for health [7,8]. Good parenting is the key to
good child development in the early years. There is a socioeconomic
gradient in domains of child development that can be observed as
young as age 3 years, including verbal ability and socioemotional
difficulties. Children from poorer households have lower scores in
verbal ability and higher scores for socioemotional difficulties than
children from wealthier households [9]. However, there was a 50%
reduction in the income gradient for socioemotional difficulties and
between 27 and 49% reductions in cognitive test score gaps when
factors indicative of good parenting (such as reading to children,
and family routines) and psychosocial influences in the home
(such as mother coping well) were taken into account.
One way to intervene in this causal chain is through support in
the early years. Good quality preschool improves educational
attainment at older ages [10]. Figure 2 shows an association
between preprimary school enrollment and school performance in
grade 6 for a number of countries in Latin America. Cuba, Costa Rica,
Equity from the start
Social conditions in early childhood have a strong impact on early
child development
One piece of evidence, based on a longitudinal cohort study in
the UK, shows an association between family socioeconomic status
and children’s cognitive developmentdchildren from advantaged
backgrounds have been shown to have a better trajectory in
cognitive development than their peers from disadvantaged
families, even overtaking by age 10 years those who were assessed
as being higher in the distribution at age 22 months (Fig. 1) [6].
This evidence is a key but does not have health as an outcome.
There is a chain of reasoning from early child development through
educational attainment, transition from education or training to
employment, good working and living conditions, income, and
better conditions at older ages. It is a chain of reasoning. It requires
a good causal model but will not be solved by one giant data set and
fancy regression equations. The chain of reasoning is backed up by a
chain of evidence [2e4]. And lived by young men like LeShawn and
Bobby [1].
Fig. 2. Association between preschool enrollment and reading scores. Tinajero
(2010) [11].
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M. Marmot, R. Bell / Annals of Epidemiology 26 (2016) 238e240
and Chile had the highest enrollment rates in preprimary education
and obtained the highest scores in school achievement at grade 6
[11]. They also are the countries in Latin America with the longest
life expectancy. Such evidence on its own does not “prove” the life
course model but it is consistent with it.
Likewise, fiscal policy to reduce poverty is almost certainly good
for healthdsee chain of reasoning. Reducing poverty through taxes
and benefits increases income, giving people more spending
power certainly, but also, more control over their lives. And when
researchers look at the effect of government welfare spending on
educational inequalities in self-reported health, they find that
countries across Europe with higher welfare spending have lower
educational inequalities in health [12].
Similarly, gender equity in education: education is the route to
empowerment, and enables men and women to have control over
their lives. Enrollment in primary education has increased
dramatically in all parts of the world in the last forty years with
improvements in gender equity in enrollment. The last forty years
have also seen dramatic increases in enrollment in secondary
education, although there are still significant gender gaps in
secondary enrollment in sub-Saharan Africa and South Asia.
Women with secondary or higher education are likely to have fewer
children than those with no education, they are more likely to make
decisions within the family, and their children are more likely to
survive and flourish.
Optimism
The United Nations Human Development Index is a composite
index of health (assessed by national life expectancy at birth,
education [mean years of schooling] and gross national income per
capita). Figure 3 shows human development index values for
countries in 2012 plotted against public expenditure on health and
education per capita in 2000. A class of graduate students could
spend a whole term arguing over the possible explanations for that
graph [1]. One of them is that if you live in the kind of society that
spends on education and health care, it is the kind of society that
will do well on human development.
Brazil has increased spending on health and education,
and achieved health equity gains through action on the social
determinants of health. One study examined stunting by family
income quintile [13]; stunting is a sign of child undernutrition, and
it causes poorer health and educational outcomes for children with
lifelong consequences. Declines in child stunting were greater
among the poorer groups, particular in the poorest group between
1996 and 2006/2007. As a result, the social gradient in stunting was
reduced dramatically. This progress in Brazil has been attributed
to socioeconomic development and equity-oriented policies,
including the Bolsa Familia conditional cash transfer system, and
increased accessed to education, health services, water, and sanitation [13].
Evidence that the social gradient in health can be reduced
should make us optimistic that reducing health inequalities is a
Fig. 3. Human development index values and previous public expenditures.
HDI ¼ human development index. UNDP (2013) [14].
realistic goal for all societies. Epidemiological thinking and
evidence from many disciplines fuels that optimism.
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