Rising unhappiness among younger people has caused the United States and some large Western European countries to fall down a global well-being index, while Nordic nations retain their grip on the top spots.

The annual World Happiness Report, launched in 2012 to support the United Nations' sustainable development goals, is based on data from U.S. market research company Gallup, analyzed by a global team now led by the University of Oxford.

People in 143 countries and territories are asked to evaluate their life on a scale from zero to 10, with 10 representing their best possible life. Results from the past three years are averaged to create a ranking.