The book argues that there are "pernicious effects that inequality has on societies: eroding trust, increasing anxiety and illness, (and) encouraging excessive consumption".[5] It claims that for 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 pregnancies, and child well-being, outcomes are significantly worse in more unequal rich countries.[1] The book contains graphs that are available online.[6]
In 2010, the authors published responses to questions about their analysis on the Equality Trust website.[7] As of December 2010, the book had sold more than 100,000 copies.[8] It has been translated into 16 languages.
In a review for Nature, Michael Sargent said that "In their new book, epidemiologists Richard Wilkinson and Kate Pickett extend this idea" (of the harm caused by status differences) "with a far-reaching analysis of the social consequences of income inequality. Using statistics from reputable independent sources, they compare indices of health and social development in 23 of the world's richest nations and in the individual US states. Their striking conclusion is that the societies that do best for their citizens are those with the narrowest income differentials—such as Japan and the Nordic countries and the US state of New Hampshire. The most unequal—the United States as a whole, the United Kingdom and Portugal—do worst."[9]
In the London Review of Books University of Cambridge lecturer David Runciman said that the book fudged the issue of its subtitle thesis of its UK first edition, and asked whether it is that “in more equal societies almost everyone does better, or is it simply that everyone does better on average?"[10] Later in the review he stated that, "More equality is a good thing and it’s an idea that’s worth defending." Richard Wilkinson responded to the review in a letter, claiming that "while pointing out that we do not have evidence on the fraction of one percent who are very rich, we show that people at all other levels of the social hierarchy do better in more equal societies".[11]
In the European Sociological Review, sociologist John Goldthorpe argued that the book relied too heavily on income inequality over other forms of inequality (including broader economic inequality), and demonstrated a one-dimensional understanding of social stratification, with social class being in effect treated as merely a marker for income. He concluded that much more research was needed to support either the Wilkinson and Pickett "account of the psychosocial generation of the contextual effects of inequality on health or the rival neo-materialist account".[12]
Richard Reeves in The Guardian called the book "a thorough-going attempt to demonstrate scientifically the benefits of a smaller gap between rich and poor", but said there were problems with the book's approach. "Drawing a line through a series of data points signals nothing concrete about statistical significance [...] since they do not provide any statistical analyses, this can't be verified." He later noted that, "The Spirit Level is strongest on Wilkinson's home turf: health. The links between average health outcomes and income inequality do appear strong, and disturbing".[13]
John Kay in The Financial Times said that "the evidence presented in the book is mostly a series of scatter diagrams, with a regression line drawn through them. No data is provided on the estimated equations, or on relevant statistical tests".[14] Boyd Tonkin, writing in The Independent, described it as "an intellectual flagship of post-crisis compassion, this reader-friendly fusion of number-crunching and moral uplift has helped steer a debate about the route to a kinder, fairer nation.[15] Will Hutton in The Observer described it as "A remarkable new book ...the implications are profound."[16] Roy Hattersley in the New Statesman called it "a crucial contribution to the ideological argument",[17] and the New Statesman listed it as one of their top ten books of the decade.[18] Charles Moore in The Daily Telegraph declared it to be "more a socialist tract than an objective analysis of poverty".[19] Gerry Hassan in The Scotsman said that Wilkinson and Pickett's claim that "more equal societies almost always do better" was "a universal, sweeping statement - which cannot be substantiated by most of their data."[20]
In 2010, Tino Sanandaji and others wrote an article for the Wall Street Journal in which they said, "when we attempted to duplicate their findings with data from the U.N. and the OECD, we found no such correlation".[21] The same group of researchers published a report for the Taxpayer's Alliance providing details of their data analysis and coming to the conclusion that "the most straightforward measure of health simply has no robust correlation to income inequality when comparing industrialized countries using standard OECD and UN statistics". Pickett and Wilkinson addressed the Wall Street Journal article in a letter to the Journal[22] and published a response to the Taxpayers Alliance report on their own site.[23]
Peter Robert Saunders, Professor Emeritus of Sociology at Sussex University, published a report for the think tank Policy Exchange questioning the statistics in The Spirit Level. He claimed that only one of the correlations in the book—that between infant mortality and income inequality—stood up to scrutiny, and that the rest were either false or ambiguous.[24] Wilkinson and Pickett published a response defending each of the claims in the book and accusing Saunders in turn of flawed methodology.[7]
Christopher Snowdon, an independent researcher and adjunct scholar at the Democracy Institute,[25][26] published a book largely devoted to a critique of The Spirit Level, entitled, The Spirit Level Delusion: Fact-checking the Left's New Theory of Everything.[27] One of its central claims is that Wilkinson excludes certain countries from his data without justification, such as South Korea and the Czech Republic. It also argues that Wilkinson and Pickett falsely claim the existence of a scientific consensus when much of the literature disagrees with their findings. Wilkinson and Pickett released a response to questions from Snowdon[28] and responded to similar criticisms in the Wall Street Journal.[22] Snowdon has in turn responded to their criticisms on his blog.[29]
In response to criticism of the book, Wilkinson and Pickett posted a note on the Equality Trust website which stated: "Almost all of the research presented and synthesised in The Spirit Level had previously been peer-reviewed, and is fully referenced therein. In order to distinguish between well founded criticism and unsubstantiated claims made for political purposes, all future debate should take place in peer-reviewed publications."[7]