These are the top 10 happiest countries in the world

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Based on a global ranking of happiness levels across 156 countries, Finland has claimed the No. 1 spot in this year's World Happiness Report.

Now in its sixth year, the World Happiness Report is produced by the United Nations Sustainable Development Solutions Network.

The organization, along with three economists from Columbia University, the University of British Columbia and the London School of Economics' Center for Economic Performance, created the report using data from the Gallup World Poll to reveal which countries are happy and why.

The report was released on March 14, less than a week before the United Nations celebrates World Happiness Day on March 20.

This year, the United States ranked No. 18 — falling four spots from last year and five from two years ago — "in part because of the ongoing epidemics of obesity, substance abuse and untreated depression," according to World Happiness Report co-editor and Columbia University professor Jeffrey Sachs.

Over the past two years, the world's top 10 happiest countries have remained the same, but have slightly shuffled positions. Through a measurement of happiness and well-being called the "Cantril ladder," Gallup asked nationally representative populations to value their lives on a scale from 0 to 10, with the worst possible life valued at 0 and the best valued at 10.

The top countries frequently have high values for all six of the key variables that contribute to overall well-being: income (GDP per capita), healthy life expectancy, social support, freedom, trust (absence of corruption) and generosity.

Here are the top 10 happiest countries and how they measure on the Cantril ladder:

1. Finland: 7.632

Senat Square in Helsinki, Finland.
Manfred Gottschalk | Getty Images

2. Norway: 7.594

Bergen, Norway
KDG | Getty Images

3. Denmark: 7.555

Copenhagen, Denmark
SeanPavonePhoto | iStock | Getty Images

4. Iceland: 7.495

Blue Lagoon geothermal pools, near Reykjavik, Iceland
Steve Allen | Getty Images

5. Switzerland: 7.487

The Swiss capital, Bern
Westend61 | Getty Images

6. Netherlands: 7.441

People attend Dutch National Tulip Day in front of the Royal Palace at Dam Square, in Amsterdam, Netherlands.
Michel Porro | Getty Images

7. Canada: 7.328

Carlo Allegri | Getty Images

8. New Zealand: 7.324

New Zealand, Auckland, Waitakere Harbour, Elevated View over Devenport towards CBD with Sky Tower at dawn
Doug Pearson | Getty Images

9. Sweden: 7.314

Stockholm, Sweden
Ellen Rooney | Robert Harding World Imagery | Getty Images

10. Australia: 7.272

The Twelve Apostles landmark off Australia's Great Ocean Road at sunrise.
Christopher Chan | Getty Images

John Helliwell, a University of British Columbia economist who co-edited the report, told The Washington Post that the most surprising finding researchers came across was "the extent to which happiness of immigrants matches the locally born population."

"The happiest countries in the world also have the happiest immigrants in the world," he added.

The report's suggestion for those who are currently unsatisfied with where they live? Learn the habits that those in the world's happiest countries have.

"The right answer is not to move to the happier communities but instead to learn and apply the lessons and inspirations that underlie their happiness. Happiness is not something inherently in short supply, like gold, inciting rushes to find and much conflict over ownership," the authors of the report state. "But happiness, unlike gold, can be created for all, and can be shared without being scarce for those who give. It even grows as it is shared."

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