I would like to use this as an opportunity to first emphasize the kind of damage that inequality does to a society. We went through a whole range of outcomes, looking at different levels of health, child well-being, and mental illness, homicide rates, imprisonment levels, teenage birth rates, drug use, kids' math and literacy scores, and social mobility in rich, developed countries, and found that all these things are worse in more unequal countries.
People, I think, have been surprised that something like income inequality can affect so many quite different outcomes. The explanation is that, basically, what we're saying is that problems related to social status within society—in that all these problems are more common at the bottom of the social ladder—get worse when we increase the social status differences in a society. They don't just get a little bit worse; these problems get anything from twice as common up to ten times as common. All these problems tend to move together in different societies, so the U.S. does worse than any of the other developed countries or nearly worse than any of the others on homicide rates, obesity rates, mental illness, drug abuse, teenage births. Life expectancy there is amongst the lowest in the developed world. All those problems are better in the more equal countries—the Scandinavian countries and Japan.
We don't have time to go into the causal mechanisms in detail, but basically what income inequality does is intensify all the ways in which class and status imprint themselves on us throughout life. The differences in performance of more and less equal societies are so large—as I say, with sometimes tenfold differences in some of these outcomes—because although these problems are worst at the bottom of society, with greater inequality the whole social fabric of a society is affected and the problems become worse amongst the vast majority.
These are not simply problems of poverty. Michael Marmot, who is perhaps the pre-eminent world expert on health inequalities, often says you can take away all the problems of poor health and poverty and still have most of the problem of health inequalities left. The health inequalities are a gradient going right across society, so even the people just below the richest have worse health than the richest. It's not a problem that you can understand simply in terms of unemployment, homelessness, and things like that. We're all part of this picture of health inequalities and also the gradients in the other problems I've mentioned.
The reason Canada does better than the U.S.A. on so many of these outcomes seems very clearly to be because you are more equal. In analyses of homicide rates and death rates from all causes, Canadian provinces come very much where you'd expect them to on the more equal end of the U.S. states.
I think people sometimes imagine—and we've had criticisms from the far right suggesting this—that we've manufactured the data by picking and choosing and so on. We never pick and choose data. We never decide what data is comparable. We simply download the data from WHO or OECD or the UN human development website, and include all the data they provide for the countries we're looking at. There's absolutely no picking and choosing. Yet, we find this consistent pattern, a tendency for more unequal countries to do worse across the whole society.
The methods we've used in our book, The Spirit Level, are very simple and straightforward because we were trying to communicate a picture to a wider public. But in medical journals in particular, the epidemiology journals, there are much more sophisticated analyses. For instance, colleagues from the Harvard School of Public Health did an analysis of multi-level models, looking at the effects of income inequality on health, after controlling for individual income and often education as well.