The Spirit Level will gird your bleeding heart in math

To appropriate a metaphor from Isaiah Berlin, some books are foxes, skipping playfully from idea to idea, while others are hedgehogs, patiently developing a single argument or theme through its pages. Richard Wilkinson and Kate Pickett's The Spirit Level is the second kind of book – a veritable Spiny Norman of a text – remorseless in its patient defence of equality.

Many of you will already be familiar with its central argument: that relative differences in income in a society are the key factor explaining health, social and environmental problems across the developed world.

Or, to put it another way – unequal societies such as the US and UK have more stress, distrust and illness compared to more income-equal countries such as the Scandanavian nations and Japan. The Spirit Level evidences this at length in graph after graph, plotting different issues against pay, slowly winding up its hedgehoggy haymaker for the intellectual knockout blow.

If the book sounds a bit like the ultima ratio regum of social democracy and the case for welfare done right, you might well have a point. But, using Japan as an example, Wilkinson and Pickett are at pains to say that relative equalities of income are perfectly compatible with a social or market-driven rather than a state-led solution. They are much more concerned with ends not means. In as far as they prescribe at all, the authors tend to see hope as lying with the co-operative movement and alternative forms of business.

The Spirit Level isn't designed to win literary awards, though it's clear, accessible and ensures readers aren't scared off by the stats. As such, I have to admit it doesn't appeal to the part of me that responds to melodrama more than means, modes and medians.

To progressives, it may also feel like exhaustive proof that the Pope is indeed 99.9999999999999999% Catholic. And boy, do Wilkinson and Pickett have a scatter graph to show you about the toilet habits of bears.

But then, you're not the readership this book needs, are you? You get it already. Rather, this is a book for use in the winning of arguments. 

A book made for making your case in political debates, in councils and ministries and for strengthening policy reports. A book to give to your economically libertarian but socially liberal friends to show them that, at the very least, the invisible hand doesn't create healthy societies of its own accord. 

A book which girds the bleeding heart in math before going to battle. 

And as such, a book which will ultimately be judged by its impact on the world rather than on your shelves.