The authors of The Spirit Level, Richard Wilkinson and Kate Pickett, are epidemiologists by training, and hold senior university posts in both Britain and the USA. Their book, the Spirit Level has been hailed as being hugely important. It investigates the incidence of health and social problems between different countries, and the relationship between those problems and income inequalities within each country. The range of problems covers many issues including imprisonment, mental health, violence, education, the status of women, and sustainability.

They have focused in particular on the 23 richest countries of the world which have populations over three million and which can provide adequate data for comparison. The big idea is that what matters in determining mortality and health in a society  is less the overall wealth of that society and more how evenly that wealth is distributed. The more equally wealth is distributed the better the health of that society.

1) In rich countries, a smaller gap between rich and poor means a happier, healthier, and more successful population.

2) Meanwhile, more economic growth will NOT lead to a happier, healthier, or more successful population. In fact, there is no relation between income per head and social well-being in rich countries.

3) If the UK were more equal, we'd be better off as a population.

For example, the evidence suggests that if we halved inequality in the UK:

- Murder rates could halve
- Mental illness could reduce by two thirds
- Obesity could halve
- Imprisonment could reduce by 80%
- Teen births could reduce by 80%
- Levels of trust could increase by 85%

4) It's not just people in poorer communities who would do better.  The evidence suggests people all the way up would benefit,
although it's true that the poorest would gain the most.

5) These findings hold true, whether you look across developed nations, or across the 50 states of the USA.