Cross cultural evidence that excessive income inequality increases rates of death & sickness, infant mortality, imprisonment, mental illness, child abuse, teenage births, failure at school, family breakup and drug abuse
It has recently become possible to compare the scale of income differences in different societies and see how the social fabric of any given 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 -- sometimes much worse -- in those societies that suffer the greatest inequality. Simply stated, those societies with the biggest income differences between rich and poor suffer a much larger range of health and social problems. The web pages that are found at the link below outline the latest 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, available at Amazon and any good book store.
Health, homicides and beyond
A review of 168 studies summarizes 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.