A new study by the University of Michigan says Canada is the ninth happiest country on Earth -- and just getting happier.

The World Values Survey, conducted by the university's Institute for Social Research, collected national surveys from 97 countries between 1981 and 2007. It found that the happiness index rose in an "overwhelming majority" of countries studied, including Canada.

Denmark came out on top as the happiest country. The U.S. came in 16th place and Canada placed ninth on the happiness scale.

The authors of the study say the reasons for Canada's strong showing are probably linked to prosperity and political freedom.

"The results clearly show that the happiest societies are those that allow people the freedom to choose how to live their lives," University of Michigan political scientist Ronald Inglehart said in a press release.

Inglehart -- the lead author of an article on the topic published this month in the journal Perspectives on Psychological Science -- said Canada is an example where tolerant social norms and a democratic political system have created higher overall happiness rates.

Over the last quarter century, the World Values Surveys, which were used as the basis of the study, have asked 350,000 two basic questions:

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

After crunching the numbers, the study's authors found that in 52 countries -- including Canada -- the happiness index rose and it fell in only 12. Researchers say that was a surprising finding.

"Most earlier research has suggested that happiness levels are stable," Inglehart said.

"Important events like winning the lottery or learning you have cancer can lead to short-term changes, but in the long run most previous research suggests that people and nations are stuck on a 'hedonic treadmill.' The belief has been that no matter what happens or what we do, basic happiness levels are stable and don't really change."

Some of the most dramatic increases in happiness occurred in countries such as India and China, which have undergone an economic boom in recent years. Zimbabwe placed at the bottom of the list.

Here is the list of the top 10 happiest countries:

• Denmark
• Puerto Rico
• Colombia
• Iceland
• N. Ireland
• Ireland
• Switzerland
• Netherlands
• Canada
• Austria