WASHINGTON - People in most countries around the world are happier these days, according to new data released Monday by World Values Survey (WVS) based at University of Michigan (UM).

Data from representative national surveys conducted from 1981 to 2007 show the happiness index rose in an overwhelming majority of nations studied, according to WVS.

The 2007 wave of the surveys provides a ranking of 97 nations containing 90 percent of the world's population. The results indicate that Denmark is the happiest nation in the world and Zimbabwe the unhappiest. The United States ranks 16th on the list, immediately after New Zealand.

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During the past 26 years, WVS have asked more than 350,000 people how happy they are, using the same two questions.

"Taking all things together, would you say you are very happy, rather happy, not very happy, not at all happy?" And, "All things considered, how satisfied are you with your life as a whole these days?"

Combining responses to these two questions, researchers constructed an index of subjective well-being that reflects both happiness and general life satisfaction.

In the 52 countries for which a substantial time series is available (covering 17 years on average), this index rose in 40 countries and fell in only 12. The average percentage of people who said they were "very happy" increased by almost seven points.

"It's a surprising finding," said UM political scientist Ronald Inglehart, who leads the surveys. "It's widely believed that it's almost impossible to raise an entire country's happiness level."

Fully as important as the fact that happiness rose is the reason. In recent decades, low-income countries such as India and China have experienced unprecedented rates of economic growth, dozens of medium-income countries have democratized and there has been a sharp rise of gender equality and tolerance of ethnic minorities and gays and lesbians in developed societies, said the survey.

As an example, Inglehart points to the tolerant social norms and democratic political systems in Denmark, Iceland, Switzerland, the Netherlands and Canada, all of which rank among the 10 happiest countries in the world.