Happy are the people of the Nordic nations — happier than anyone else in the world. And the overall happiness of a country is almost identical to the happiness of its immigrants.

Those are the main conclusions of the World Happiness Report 2018, released Wednesday. Finland is the happiest country, it found, followed by Norway, Denmark, Iceland, Switzerland, the Netherlands, Canada, New Zealand, Sweden and Australia. Though in a different order, this is the same top 10 as last year, when Norway was No. 1 and Finland was fifth.

The least happy nations: Burundi and Central African Republic, both consumed by political violence.

As for the United States, it is 18th out of 156 countries surveyed — down four spots from last year’s report and five from 2016’s, and substantially below most comparably wealthy nations. Though the economy is generally strong and per capita income is high, it ranks poorly on social measures: Life expectancy has declined, suicide rates have risen, the opioid crisis has worsened, inequality has grown and confidence in government has fallen.

“I think there really is a deep and very unsettling signal coming through that U.S. society is in many ways under profound stress, even though the economy by traditional measures is doing fine,” said Jeffrey D. Sachs, an editor of the report. “The trends are not good, and the comparative position of the U.S. relative to other high-income countries is nothing short of alarming.”

The report was produced by the United Nations Sustainable Development Solutions Network and edited by three economists: Sachs, the network’s director and a professor at Columbia University; John F. Helliwell, a senior fellow at the Canadian Institute for Advanced Research and professor emeritus at the University of British Columbia; and Richard Layard, a director of the Well-Being Program at the London School of Economics’ Center for Economic Performance.

It is based on Gallup International surveys conducted from 2015 to 2017. The report cites six significant factors in its measure: gross domestic product per capita, social support, life expectancy, freedom to make life choices, generosity and corruption levels.

It said a person who moves to a country high on the happiness list will probably become happier, and a person who moves to a lower-ranked country will probably become less happy.

In countries with high migrant acceptance indexes — that is, countries where the populace is generally receptive to newcomers — immigrants “are happier than their other circumstances would indicate, and so were the people who were born there,” Helliwell said. “That sort of openness turns out to be good for both.”