- Low-income countries (particularly India and China) have experienced unprecedented rates of economic growth, pulling millions of people out of poverty;
- Democracy has been introduced in many countries, and become stronger and more entrenched in countries that were partially democratic;
- Increasing gender equality;
- Increased tolerance of ethnic minorities and gays and lesbians in developed societies.
Rich countries tend to be happier than poor countries. And according to University of Michigan political scientist Ronald Inglehart, who headed up the survey, "The results clearly show that the happiest societies are those that allow people the freedom to choose how to live their lives."
Of the countries surveyed, Denmark is the happiest and Zimbabwe the most miserable. The US ranks 16th.