For its 2018 World Happiness Report, the Sustainable Development Solutions Network (SDSN) for the United Nations studied 156 countries and considered six variables: GDP per capita, healthy life expectancy, social support, perceived freedom to make life choices, perceptions of corruption and generosity. These were rated on a scale from 1 (worst) to 10 (best). We count down the 20 unhappiest and the 20 happiest nations.

Score: 4.139. Sudan has long suffered from conflict due to civil war in the country. Residents here have a low life expectancy and little freedom to make choices.

Score: 4.103. The population of Ukraine is reducing due to low birth rates and increased male mortality. People in the second largest country in Europe fear corruption the most.

Score: 3.999. Located in West Africa’s Gulf of Guinea, Togo residents experience low life expectancy. Although the country has shot up 15 places from last year, corruption remains a major concern.

Score: 3.964. This country has been ravaged by the Ebola virus, violent ethnic clashes, and an influx of refugees from Liberia and Sierra Leone, putting a strain on its residents. However 2018 looks to be a slightly better year as it has moved up 10 places in the World Happiness Report.

Score: 3.808. The Kingdom of Lestho is made up mostly of highlands, where most villages can only be reached by horseback. Life expectancy is low as resources are minimal and the environment is harsh.

Score: 3.795. This African nation that borders Namibia, Zambia and the Democratic Republic of the Congo can thank years of widespread government corruption and devastating poverty for its ranking. Life expectancy here is one of the lowest in the world, with one in six children dying before the age of five. Down two places on last year, it is easy to see why.

Score: 3.774. Located off the southeast coast of Africa, Madagascar has jumped up four places in the last year. Despite having decent social support, it scored low in freedom, generosity and perceptions of corruption.

Score: 3.692. It's easy to see why the country of Zimbabwe has a low GDP per capita. The cash-strapped economy faces severe challenges, with unemployment and poverty both pandemics. Many people have left the country in search of work in South Africa.

Score: 3.632. Landlocked Afghanistan lies in the middle of a hotbed of corruption and conflict which explains its 12th place on this list. Afghans scored low in all areas especially social support, despite moving up from 4th least happy country last year.

Score: 3.590. Botswana is one of Africa's most stable countries politically, and its biggest producer of diamonds. It once had the world's highest rate of HIV-Aids infection, which has improved. However, it still has a low life expectancy.

Score: 3.587. A largely agricultural country, Malawi scores low in all six factors, but has a noticeably low GDP per capita

Score: 3.582. The continuing political crisis in Haiti hinders the government's ability to meet the basic needs of its people. After Hurricane Matthew in 2016, a food crisis hit the devastated country.

Score: 3.495. Africa’s oldest republic has stayed put at eighth place since last year. Devastated by a violent civil war, where around 250,000 people were killed, Liberia has one of the lowest GDPs per capita of any nation.

Score: 3.462. Despite having incredibly low levels of freedom and social support, the country, which has been ravaged by militant groups like ISIS and the Al-Qaeda affiliate Jabhat al Nusra, has one of the highest GDP per capita and life expectancy of any other nation in the bottom 20. Surprisingly it has moved up five places from the second least happy country last year.

Score: 3.408. The small landlocked country in east-central Africa still struggles to recover from the devastating genocide that struck in the mid-1990s. As a result, the nation sits in sixth place on the list, the same as last year, with low life expectancy, social support and GDP per capita.

Score: 3.355. Boarding Saudi Arabia and Oman, Yemen has become a base for militant groups like Al-Qaeda and the so-called Islamic State, adding to the violence and instability in the country. Down six places from 2017, the nation’s people enjoy a relativity high GDP per capita compared with other countries in the bottom 20 but it struggles with a reputation for corruption.

Score: 3.303. While the country has been spared the internal strife many of its neighbouring states struggle with, it has been knocked down by five places on last year's survey. Much of the population live below the poverty line. As a result, life expectancy is incredibly low.

Score: 3.254. According to the United Nations war-ravaged South Sudan is facing possible famine, which may be why it has leapt from 15th place to third this year. Two years of civil war, which has claimed the lives of four million people, has left life expectancy low and corruption levels high.

Score: 3.083. The Central African Republic has been unstable since its independence from France in 1960. With one of the world's poorest populations it has incredibly low levels of social support and GDP per capita.

Score: 2.905. According to the report, Burundi residents have been the least happy people in the world for two years running. Although it scores poorly in every category, it is particularly scarred by high levels of corruption from both the regional police and the judiciary system. Now let’s turn our attention to the 20 happiest nations on earth.

Score: 6.774. One of the Middle East's most important economic centres, the United Arab Emirates has an incredibly high GDP per capita and feeling of freedom. This could be due to it being one of the more liberal countries in the Gulf area.

Score: 6.814. The United Kingdom is an economic and military power with great political and cultural influence around the world. It has low levels of corruption and high social support.

Score: 6.886. It might be called the land of the free, but US citizens struggle with their perception of corruption levels within the country. That said, they have a high GDP per capita, excellent social support and are fairly generous. However, the country has dropped from 13th place last year.

Score: 6.910. Despite having a population of just 550,000, Luxembourg boasts the highest GDP per capita in the top 20. It's moved up three places on last year's survey.

Score: 6.927. The Belgians are a pretty happy bunch of people according to the World Happiness Report. This hasn't changed much in the space of a year, with the country moving from 18th to 16th place. The reason? People feel they can rely on one another for strong social support and feel free to live their lives the way they wish.

Score: 6.965. The Germans have moved down one spot in 2018, however they can still rely on their neighbours as they enjoy high levels of social support. They’re also a wealthy bunch with strong GDP per capita.

Score: 6.977. Ireland’s economy is doing very in 2018, according to the World Happiness Report. Happiness levels are boosted thanks to strong social support within the community and people's generosity to each other. Overall, the country is doing better than last year, having moved from 19th spot.

Score: 7.072. Costa Rica shows that money doesn’t buy happiness with Professor Jeffrey Sachs, head of the SDSN and special advisor to former UN Secretary General Ban Ki-moon, calling the island nation ‘an example of a healthy, happy society [despite not being] an economic powerhouse’.

Score: 7.139. While the alpine country scores highly in the areas of GDP per capita and the freedom to make life choices, its people could stand to be a little more generous. Not much has changed in the last year as it has remained in 12th place.

Score: 7.190. While many of their neighbouring countries ranked low on the list, Israel is continuing to stand out from the pack, remaining in 11th place, with its citizens experiencing a high GDP per capita, good social support and a high life expectancy.

Score: 7.272. The folks Down Under are pretty satisfied with their lives, still scoring highly across all six categories from their ninth place in 2017. In particular, they are a wealthy bunch with a high GDP per capita and they’ll have a long time to enjoy it with the nation recording a high life expectancy.

Score: 7.314. Western Europe’s third largest country has swapped places with Australia among the ranks. And why wouldn’t Swedes be happy with high GDP per capita, strong social support amongst its citizens and solid healthcare boosting their life expectancy?

Score: 7.324. Coming in at number eight, the same as last year, the land of the long white cloud edged ahead of its Antipodean neighbour Australia. The small island country's residents prove they’re a tight-knit bunch that like to look out for one another, scoring highly for generosity and social support.

Score: 7.328. With a high life expectancy and good average income, Canada comes in as the seventh happiest country, down one spot from last year.

Score: 7.441. With people's liberal views and good work/life balance, it’s not surprising that the Netherlands moved up a spot on the index since 2017.

Score: 7.487. It may have dropped three places from the second happiest country last year, but Swiss people still have many reasons to smile. The nation’s people enjoy a high GDP per capita, strong social support and feel they have the freedom to make their own life choices.

Score: 7.495. The 2018 survey showed that despite Iceland suffering from the post-2007 economic crisis the country’s residents are still able to maintain extremely high levels of happiness largely because of social support and solidarity.

Score: 7.555. The Scandinavian nation took top spot as the world’s happiest country last year. Despite dropping to third this time around, it still scores highly across all six categories in the report, particularly in the areas of social support, life expectancy and low levels of corruption.

Score: 7.594. Coming in at second place with one of the highest GDPs on the list, Norway is among the wealthiest countries and that’s reflected in its residents' quality of life. Norway also boasts one of the highest life expectancies.

Score: 7.632. And we have our winner. While they might not be as generous as their European neighbours, Finns enjoy wealthy and healthy lives, believe their country has low levels of corruption and enjoy the freedom to make their own life choices.