Each country's happiness score was computed based on multiple variables, including per capita gross domestic product, social support, life expectancy and freedom from corruption. The index ranked countries by how happy their citizens perceive themselves to be, according to their evaluations of their own lives.
"It's true that past year all Finns were happier than rest of the countries' residents, but their immigrants were also happiest immigrants in the world", said the report's co-editor and professor emeritus of economics at the University of British Columbia John Helliwell told CNN.
Other notables included Australia (11), the United Kingdom (15), Germany (17), the USA (19), Mexico (23), Brazil (32), South Korea (54), Japan (58), Russian Federation (68), Nigeria (85), Indonesia (92), China (93) and India (140).
At the other end of the happiness index was South Sudan in Africa.
That's partly explained by "dramatic falls" in happiness in population dense countries like the United States, Egypt and India, it said. "But the response of New Zealand's people to the attacks does".
The top five happiest countries in the world are Europe's Nordic nations, Finland (7.769), Denmark (7.600), Norway (7.554), Iceland (7.494) and Netherlands (7.488).
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It came 15th while Ireland came in 16th place.
"The world is a rapidly changing place", said Professor John Helliwell, co-editor of the report.
Addiction is partly to blame, says report co-author Jeffrey Sachs, director of the Sustainable Development Solutions Network, who wrote a chapter focused on the U.S. epidemic of addictions and unhappiness in America, a rich country where happiness has been declining.
Finland is once again the world's happiness nation.
On the other hand, Rwanda is the fifth most miserable country in the world after South Sudan, Central Africa Republic, Tanzania and Afghanistan which have suffered war for a long time apart from Tanzania.