Wellbeing is mainly studied by asking people questions. The most common question is about life-satisfaction and replies satisfy standard tests of reliability and validity. Using the Gallup World Poll, the World Happiness Report finds that on a scale of 0–10, 1 in 6 of the world’s population score 3 of below and 1 in 6 score 8 or above – a huge inequality in the quality of life. Another approach is to measure how people feel from moment to moment – their ‘affect’. This can be done by bleeping people in real time or asking retrospective questions about yesterday. This approach is best for measuring the effects of short-term experiences, but less so for measuring a person’s underlying wellbeing. The book rejects the third so-called ‘eudaimonic’ measure of wellbeing, on the grounds that virtue is the means to an end (and not the end itself).

People’s wellbeing is experienced by how far their needs are satisfied. This depends on what they bring to the table (their behaviour, their thoughts, and their genes) and by the social environment in which they live. This determines the structure of Parts II and III of the book. Part IV deals with the role of government.

Wellbeing varies hugely in the human population. About 80% of this variance is within countries and about 20% is between countries. Between 1980 and 2007 average wellbeing rose in more countries than where it fell. But since 2008 wellbeing has fallen in roughly the same number of countries as where it has risen. Since 2006/8 there has been a large worldwide increase in negative affect and in stress. In the US the inequality of wellbeing is one of the highest in the OECD, whereas Europe (since 2008) now has lower wellbeing inequality than any other region.

Average wellbeing is very similar for men and women in almost every country. It declines with age in most parts of the world but in North America and Europe it improves after mid-life. Average wellbeing is below average for most ethnic minorities in most countries. Children’s wellbeing is lower in the UK, the United States and Japan than in most other OECD countries. Meanwhile, adult life-expectancy has risen in most regions of the world, especially in Sub-Saharan Africa. So the Wellbeing-Years (WELLBYs) which a person now born can expect have increased since 2006–8 in all regions of the world.