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.