Over half a century ago, social policy research clearly demonstrated the problem of poverty in an unequal society, a problem that has never really gone away (Titmuss, Reference Titmuss1938). More recently, one particular book has done much to champion the cause for greater equality. In so doing, it has reignited old debates about poverty and inequality in new and important ways. That book is of course The Spirit Level by Richard Wilkinson and Kate Pickett – a book that has made a rare transfer from the academic world into the public domain, selling over 200,000 copies and with translations in more than twenty languages. The Spirit Level (currently) has over 2,000 citations on Google scholar and Richard's TED talk has over 1.6 million viewings, making the importance of this work beyond question. In fact, The Spirit Level is probably the most influential book in social policy published in the last decade.

The research argues, and attempts to demonstrate, that societies that are more unequal experience significantly worse health and social problems. The study uses data for twenty-three rich countries across a range of well-being measures:

1. 1. physical health (life expectancy)

2. 2. mental health/illness

3. 3. drug and alcohol addiction

4. 4. children's education performance

5. 5. imprisonment rates

6. 6. obesity

7. 7. social mobility

8. 8. level of trust

9. 9. homicides

10. 10. teenage birth rate, and

11. 11. infant mortality.

Building on earlier work (e.g., Wilkinson, Reference Wilkinson2005; Wilkinson and Pickett, Reference Wilkinson and Pickett2006), Wilkinson and Pickett provide a range of statistical evidence to support their view that inequality is bad for society. They largely do this by using simple (but no less compelling) correlation techniques that suggest a link between income inequality at the country-level and many of their wellbeing indicators, as well as weak relationships between national average income per person and their index of health and social problems. ‘Inequality has pernicious effects on societies’, the authors observe, ‘eroding trust, increasing anxiety and illness, encouraging excessive consumption’.

The statistical evidence, the authors argue, makes an irrefutable case for greater equality. What is more, the transformation of our societies requires a social movement that demands greater equality towards improving the quality of life for all. The Equality Trust – a not-for-profit organisation that Wilkinson and Pickett co-founded – promotes the evidence on why inequality matters, arising out of The Spirit Level and you can also sign their Equality Charter (www.equalitytrust.org.uk). All of which is very laudable and welcome in Social Policy circles.

Their statistical evidence, however, is fiercely disputed (Saunders and Evans, Reference Saunders and Evans2010; Snowdon, Reference Snowdon2010). Saunders and Evans, for example, speak of ‘wonky statistics’ and ‘spurious correlations’. In sum, the associations in their graphs linking high levels of income inequality with health and social problems between countries are called into question. The ‘clustering’ of countries in The Spirit Level has also been criticised (familiar to Social Policy as the different ‘worlds’ or ‘regimes’ of welfare). The Nordic countries often appear at one end of the graphs (doing well), and the (less equal) Liberal cluster often appears at the other end (doing less well).

In this review it is not necessary to get drawn into some of the (rather sterile) debates about whether excluding a particular high income country or set of high income countries as ‘outliers’ alters the fit of a regression line in a simple linear regression model or not. Besides, many of the issues over ‘selectivity’ already appear to be have been dealt with; Saunders’ picking and choosing in his work is far more selective of countries than Wilkinson and Pickett (Rowlingson, Reference Rowlingson2011).

Instead, and this is the point I really want to emphasise, The Spirit Level has helped to motivate important new research and findings on social inequality. In The Spirit Level, Wilkinson and Pickett present a social or environmental contextual argument relating inter-country variations in health and social outcomes to income inequality. According to the authors, the reason why inequality causes an increase in social problems in more unequal societies is people's perceptions of inferiority or status anxiety. Inequality is a relative experience, which implies that people evaluate their wellbeing compared with a reference point. Richard Layard (Reference Layard2005) makes a similar argument about our frustration, and unhappiness, in the social context of trying to ‘keep up with the Joneses’, and W.G. Runciman famously before that (Runciman, Reference Runciman1966). Still others maintain that individual compositional factors – particularly the lack of personal income or poverty – within society matters greatly for the health and wellbeing of those experiencing deprivation (Jen et al., Reference Jen, Jones and Johnston2009). In other words, it is not just the politics of ‘envy’ or ‘greed’ at play in rich societies, if at all, but the material deprivation experienced by people living in society.

Answers to such fundamental, but complex questions matter and have been at the heart of Social Policy debate for far too long; hopefully, there will be further opportunity to address some of them under the current New Opportunities for Research Funding Agency Cooperation in Europe call on Welfare State Futures and Inequalities (www.norface.net [Theme 2]). NORFACE is a partnership between fifteen research councils, including the UK's ESRC, to increase cooperation in research and policy in Europe.

Certainly, there are good grounds for optimism; we now have access to high quality datasets, from social surveys and administration systems that span the globe, as well as sophisticated multilevel modelling techniques (www.bristol.ac.uk/cmm) that did not exist when my mentors – Jerry Morris and Peter Townsend – were mapping out this terrain (Black et al., Reference Black, Morris, Smith and Townsend1980).