The Spirit Level

"Research by Richard Wilkinson and Katie Pickett has shown that among the richest countries, it's the more unequal ones that do worse according to almost every quality of life indicator," soon-to-be Prime Minister David Cameron said in 2010, a few months before the election.

He referred to The Spirit Level, the 2009 best-selling book by social epidemiologist Richard Wilkinson and epidemiologist Kate Pickett. It suggested that countries with the biggest gap between the rich and the poor have the highest level of health and social problems – and that everyone in an unequal society (and not just the poor) are negatively affected. It causes shorter, unhealthier and unhappier lives, and problem issues will simply not go away unless we tackle inequality, the researchers argue.

Wilkinson and Pickett compiled information from data from 23 countries and 50 US states, with sources including the United Nations, the World Bank, the World Health Organisation and the US Census. Arranging the data in a series of scatter-graphs they revealed a consistent pattern across a wide range of issues connected to wellbeing and quality of life. It showed a strong correlation between a country's level of economic inequality and its social outcomes. Japan and the Scandinavian countries scored consistently well at the 'low' end (low levels of inequality and low levels of social problems) while the UK, the US and Portugal were at the unfavourable 'high' end.

Critics argue that the use of statistics is overly simplistic, ignoring more complex relationships and drawing conclusions with insufficient data. The Spirit Level remains a debated work, but did bring inequality fully into the public debate and to the attention of senior policymakers – becoming a bestseller in the process.