The world’s happiest countries are also the world’s least religious countries according to a new report released by the World Happiness Index.

Science Alert reports that every year, the World Happiness Index surveys numerous people from various countries around the world in search of, as the name implies, which country has the happiest population. This year’s winner is Denmark, followed closely by Switzerland, Iceland, and Norway. The US ranked 13th.

The report shows that the world’s happiest countries are also the world’s least religious countries. The happiest countries also tend to be fairly homogeneous nations with strong social safety nets.

The report explains how researchers determined their list ranking the world’s happiest countries:

The rankings are based on answers to the main life evaluation question asked in the poll. This is called the Cantril ladder: it asks respondents to think of a ladder, with the best possible life for them being a 10, and the worst possible life being a 0. They are then asked to rate their own current lives on that 0 to 10 scale.

According to the report, released Wednesday (March 16), Denmark has reclaimed its place as the world’s happiest country, while Burundi ranks as the least happy nation.

Denmark topped the list in the first report, issued in 2012, and again in 2013, but it was displaced by Switzerland last year.

In this year’s ranking, Denmark was back at No. 1, followed by Switzerland, Iceland, Norway, Finland, Canada, the Netherlands, New Zealand, Australia and Sweden.

The unhappiest countries in the world are Afghanistan at 154th followed by Togo and Syria. Burundi comes in last at 157th.

While the study shows a correlation between happiness and non-religiousness, no causal relationship is demonstrated. One can only speculate if it is the lack of religion that makes countries happier, or that happy countries simply reject religious superstition.

Anecdotal evidence would suggest that unhappy people are driven to religion, given the fact that when one is unhappy in this life they can embrace the idea that there is something better waiting for them after death.

The 2016 World Happiness Report seeks to quantify happiness as a means of making societies healthier and more efficient.

Bottom line: The world’s happiest countries are also the world’s least religious countries.