Beware False Prophets : Equality, the Good Society and The Spirit Level (2010) by Peter Saunders is a remarkable investigation of the claims made in the book The Spirit Level by Richard Wilkinson and Kate Picket. In The Spirit Level it is claimed that inequality drives a range of social ills ranging from health to crime and suicide. They claim that reducing inequality drives all these things and that reducing inequality is required because of this.
Saunders takes the claims to pieces. He goes through their 20 claims, shows that 14 are spurious or invalid and in only one case, infant mortality are their claims very strong supported.
Saunders uses a variety of techniques to point out the problems. For a number of indicators a few countries drive the whole association. The homogeneous Scandinavian countries and Japan are more equal than most rich countries and do well on a number of social indicators. The US, which is less equal, does badly. If these two groups are removed the remained of the data set often does not, as it should, exhibit any correlation between the inequality and the various social outcomes.
The Spirit level also does similar tests on US states. Again, however, a cultural pattern of Southern and other states dominates many of the social problems. If split into two parts neither exhibit the same correlation as the whole. Again, a cultural difference is expressed both as higher income inequality and poorer social outcomes.
Saunders also points to the results of Australian academics who have pointed out that if income inequality drove various social ills then as it varied over time the social ills should. This also does not happen.
Saunders also points that the debunking of the claims of the Spirit Level does not remove the case for reducing inequality. Income inequality is still an important issue that society needs to respond to. But the claims that are made by the Spirit Level are not justified by the data.