Personal freedom is more important than money, the authors say
Denmark is the happiest country in the world, according to the latest World Values Survey published by the United States National Science Foundation.
The annual study surveyed people in 97 countries to discover who is happiest.
The survey asked people two simple questions about their happiness and their level of satisfaction with life.
Puerto Rico and Colombia completed the top three happiest nations. Zimbabwe was found to be the least happy, with Russia and Iraq also in the bottom 10.
The study was directed by University of Michigan professor Ronald Inglehart. He says that unlike other studies, which have focused on economic factors, his research has found that financial prosperity is not the only reason for happiness.
"Our research indicates prosperity is linked with happiness. It does contribute," he says, "but it is not the most important factor.
"Personal freedom is even more important, and it's freedom in all kinds of ways. Political freedom, like with democracy and freedom of choice."
A happier world
The world is becoming a happier place overall, according to the survey, which has been conducted since 1981.
Zimbabwe has suffered hyperinflation and political violence.
Dr Inglehart says that gender equality is also an indicator of happiness, as is rising social tolerance. He says that both of these things have risen dramatically in recent years.
The world's wealthiest nation, the United States, was found to be the world's 16th happiest country, behind Switzerland, Canada and Sweden.
The study also found that the countries at the bottom of the list all struggle with widespread poverty or authoritarian governments.
Zimbabwe, which is gripped by hyperinflation, and has recently seen a controversial presidential election marred by violence, was found to be the least happy nation amongst the countries covered by the survey.