The report was produced by the United Nations Sustainable Development Solutions Network and edited by three economists: Dr. 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, in which thousands of respondents were asked to imagine a ladder with steps numbered 0 to 10 and to say which step they felt they stood on, a ranking known as the Cantril Scale.
The top 10 countries’ averages ranged from 7.632 for first-place Finland to 7.272 for 10th-place Australia; the United States’ average was 6.886, down from 6.993 last year. At the bottom of the scale, Burundi’s average was 2.905.
Compared with a 2008-10 base period, 58 countries became significantly happier, and 59 became significantly less happy. Of the 141 countries that had enough data from both 2008-10 and 2015-17 to measure how their happiness had changed, the United States ranked 107th, with a drop of 0.315 in its average happiness rating.
Explaining why one country is happier than another is a dicey business, but the report cites six significant factors: G.D.P. per capita, social support, life expectancy, freedom to make life choices, generosity and corruption levels.
Dr. Sachs noted that the happiest countries have very different political philosophies from the United States’. Most of the top 10 are social democracies, which “believe that what makes people happy is solid social support systems, good public services, and even paying a significant amount in taxes for that.”
This year’s report also focused heavily on how migration affects happiness. Most notably, it found that the happiness of a country’s immigrants is almost identical to that of its population at large — indicating, Dr. Helliwell said in an interview, that “people essentially adjust to the average happiness level of the country they’re moving to.”
“The closeness of the two rankings shows that the happiness of immigrants depends predominantly on the quality of life where they now live,” the report’s executive summary said. “Happiness can change, and does change, according to the quality of the society in which people live.”
This cuts both ways: 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.
The study did not examine how national immigration policies affect happiness. However, it did examine the findings of Gallup’s new “migrant acceptance index,” which measured public attitudes toward immigrants in various countries. These attitudes are not always correlated with national policies: The United States, for example, ranks highly on the migrant acceptance index, even though the Trump administration has pursued more restrictive immigration laws.
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,” Dr. Helliwell said. “That sort of openness turns out to be good for both.”