Finland has topped a list of the world's happiest nations for the sixth successive year. 

The northern European nation was judged to be the happiest, according to the World Happiness Report 2023, an annual report published by United Nations' initiative, the Sustainable Solutions Network, since 2012.

Here's how they determine which nation is the happiest, and where Australia is ranked: 

How are the different countries ranked?

To measure happiness, the report uses survey data taken from the Gallup World Poll asking respondents from each country to evaluate their life satisfaction over the previous three years. 

Specifically, these life evaluations ask survey respondents to evaluate their current life, from 0 to 10, in comparison to the life they'd ideally like to be living.

"They are then asked to rate their own current lives on that 0 to 10 scale."

This year's happiness rankings are based on the three-year average of these life evaluations taken in 2020, 2021 and 2022.

So they are particularly instructive of how happy specific national populations felt during the COVID-19 pandemic. 

The Gallup World Poll typically takes a sample of 1,000 respondents from each country. 

What makes some countries happier than others?

According to the World Happiness Report there are six factors that help explain countries' varying degrees of happiness.

The report's modelling found these six variables all play a strong role in supporting respondents' life evaluations, accounting for more than three quarters of variation in respondent answers:

GDP per capita: Gross Domestic Product, or how much each country produces, divided by the number of people in the country.

Healthy life expectancy: Based on World Health Organisation data, this takes into account how long a person's life is, but also their physical and mental health throughout their life.

Social support: The World Happiness report defines this as having someone to count on in times of trouble, with respondents asked: "If you were in trouble, do you have relatives or friends you can count on to help you whenever you need them, or not?"

Freedom to make life choices: Based on the question "Are you satisfied or dissatisfied with your freedom to choose what you do with your life?", participants are asked to take into account all human rights inherent to human beings regardless of race, sex, nationality, ethnicity, language or religion. It also includes the right to life and liberty, freedom from slavery and other torture, freedom of opinion and expression and the right to work and education.

Generosity: This variable concerns how willing citizens are to help their fellow humans, with respondents asked: "Have you donated money to a charity in the past month?" The authors cite research that shows that, in all cultures, starting in early childhood, people are drawn to behaviours that benefit other people.

Perception of Corruption: This goes beyond whether a government is outwardly corrupt or not. It asks participants if they trust their government as well as their country's businesses to act in a way that is not corrupt.

What are the least-happy countries?

Afghanistan, which came 137th, was ranked the least-happy country, followed by Lebanon, Sierra Leone, Zimbabwe, Democratic Republic of Congo, Botswana, Malawi, Comoros and Tanzania.

How does Australia rank?

Australia ranks in 12th place, just behind New Zealand and Austria, and ahead of Canada, Ireland, US and Germany. 

What trends were recorded?

According to the report, most populations around the world continue to be remarkably resilient, despite several crises, such as the COVID-19 pandemic, global energy crisis, high inflation and the war in Ukraine.

They base this conclusion on the fact that the 2020 to 2022 global life evaluation averages remain just as high as those in the pre-pandemic years of 2017 to 2019.

More generally, it says people are happier living in countries where the gap between the happiest and the unhappiest respondents in a nation is smaller.

The report says the same nations typically appear in the top-20 list year after year.

One exception is Lithuania, which has risen over the past six years from being ranked 52nd in 2017 to number 20 in this year's report.