France, March 19 -- Published on Thursday by the University of Oxford's Wellbeing Research Centre, the annual World Happiness Report paints a mixed picture.

Life satisfaction scores among under-25s in countries including the United States, Canada, Australia and New Zealand have dropped markedly over the past decade. On average, scores among young people in English-speaking and Western European countries have fallen by nearly one point on a scale from 0 to 10.

Researchers point to heavy social media use as a possible contributing factor. One survey of 15-year-olds found those who spend five hours or more per day on social media reported noticeably lower life satisfaction than those who use it less.

However, the relationship is not strai...