Wilkinson and Pickett explain that as epidemiologists, they research the causes of diseases in human populations. They were inspired to write The Spirit Level after performing decades of research into why and how people with different incomes have different health outcomes and life expectancies. In addition to their own research, the authors also rely on other studies, as well as international income and health statistics to support their argument. The authors acknowledge that social science arguments are always more controversial than physical science findings because everyone has their own opinions about how society functions. Pickett and Wilkinson are optimistic that their readers will agree that all societies should work to reduce inequality.

While citizens of developed countries enjoy unprecedented material wealth and convenience, many struggle with unbridled consumerism, anxiety, depression, and social detachment. The authors argue that this malaise contributes to unhealthy, comfort-seeking behaviors, such as overeating and addictions. The authors interpret these trends as symptomatic of “social failure” (3). Pickett and Wilkinson contend that mainstream political narratives encourage voters to consider their individual needs and status within society and have failed to paint a picture of a better society in general or a plan to achieve it. The authors argue that this “social failure” in materially rich countries is a sign that governments must prioritize the psychological well-being of people at every level of their society (3).