Tornado Alley (PROG)

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The Evidence

Below you will find a detailed introduction to the evidence. If you are new to this issue, you may wish to begin by reading a short overview.

An introduction from Richard Wilkinson & Kate Pickett

Richard and KateGreat inequality is the scourge of modern societies. We provide the evidence on each of eleven different health and social problems: physical health, mental health, drug abuse, education, imprisonment, obesity, social mobility, trust and community life, violence, teenage births, and child well-being. For all eleven of these health and social problems, outcomes are very substantially worse in more unequal societies.

We have checked the relationships wherever possible in two independent test beds: internationally among the rich countries, and then again among the 50 states of the USA. In almost every case we find the same tendency for outcomes to be much worse in more unequal societies in both settings.

We also present evidence on four other important issues. One is how achieving greater equality within the rich countries may contribute to tackling the inequalities between rich and poor countries. Another is a discussion of both the compatibility and relative merits of greater equality and economic growth as sources of improvements in the quality of life among rich countries. There is a page discussing how greater equality may contribute to policies designed to tackle global warming, and lastly, a page (The Remedies) pointing out that there are many different ways of increasing equality in our societies.

The data we use comes from the most respected international sources including The World Bank, World Health Organisation, United Nations, UNICEF, and US Census Bureau. Much of this work has already been published in peer reviewed academic journals, and some of the relationships have been tested many times by different research groups using data for different societies.

Details of the data and statistical techniques we use are available on the Statistical Sources and Methods page and the international dataset can be downloaded here.

A full description and explanation of this research is now available as a book: Richard Wilkinson and Kate Pickett, The Spirit Level (Penguin). Buy the book from Amazon. [external link]
The authors explain their findings

The effects of inequality

Until recently, most of the argument about the scale of income inequality in modern societies has been about fairness and unfairness. But it has recently become possible to compare the scale of income differences in different societies and see how the social fabric of society is affected by how much inequality there is. Research using this data carried out since the early 1990s shows that many of the most pressing health and social problems are worse in more unequal societies - often much worse. Societies with bigger income differences between rich and poor seem to suffer more of a very wide range of health and social problems. These web pages outline the evidence and tell you where to find more detailed summaries and research reports. A straight forward outline of all the material can be found in a book written by Richard Wilkinson and Kate Pickett, called The Spirit Level, published by Penguin. Buy the book from Amazon. [external link]
Health, Homicides and beyond

The first indications of the harmful effects of inequality came almost simultaneously from research on health and on homicides. A review of 168 studies summarises the evidence internationally among rich and poor countries as well as for regions, states, and cities within many different countries. The tendency for more unequal societies to have worse health has been found for many different health indicators, including age-specific death rates, infant mortality, life expectancy, and illness.

More recently we have found that the same pattern applies to most of the social problems which, within countries, tend to be concentrated in the most deprived areas and become more common further down the social ladder. Like violence and ill health, they are all much more common in more unequal societies. So far the evidence covers mental illness, drug abuse, teenage births, obesity, the proportion of the population in prison, educational performance of school children, levels of trust and strength of community life, and social mobility.

Some of the relationships with inequality have been demonstrated many times in peer reviewed research publications. Almost all have been shown in at least two different tests beds: internationally among a group of the richest countries, and independently among the 50 states of the USA. We should emphasise that when we talk about the effects of inequality that we do not mean the effects of poverty or low average incomes.
Big differences, everyone affected

One of the most striking and important features of these relationships is that the differences in the prevalence of the various social problems are so large. Some are two or three times as common in more unequal societies, but others are as much as ten times as common. The evidence suggests that this is partly because inequality affects the vast majority of the population - not just the poorest.

Finally, it tends to be the same societies which do well on each of the different outcomes just as it is the same ones which do badly. Because inequality affects so many different outcomes, if you know that a society does badly - for instance - on health, it is likely that it also does badly on a wide range of social problems: it probably has high levels of violence, high teen birth rates, a high prison population, lower levels of trust, more obesity, and a bigger drug problem. It looks as if societies with large income inequalities become socially dysfunctional.

Overviews of the bare facts and statistical evidence can be found in:-

Wilkinson RG, Pickett KE. Income inequality and health: a review and explanation of the evidence. Social Science and Medicine 2006; 62: 1768-84. [PDF]

A fuller discussion of the evidence and of the causal social processes through which inequality has these effects can be found in:-

Wilkinson RG. The Impact of Inequality: how to make sick societies healthier.
http://www.equalitytrust.org.uk/why/evidence