Quote:
The Evidence

Great 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.*

http://www.equalitytrust.org.uk

Thought this was an interesting attempt at arguing for more equal societies with hard evidence of the effects. (Though they point to their book an awful lot.)

Their methods are described here. There's also lots of charts comparing countries with things like infant mortality rates.

Anyway, looked like it could be a handy reference source.