Populists across the world are significantly more likely to believe in conspiracy theories about vaccinations, global warming and the 9/11 terrorist attacks, according to a landmark global survey shared exclusively with the Guardian.

The YouGov-Cambridge Globalism Project sheds new light on a section of the world population that appears to have limited faith in scientific experts and representative democracy.

Q&A What is the YouGov-Cambridge Globalism Project? Show Hide The project is a new annual survey of global attitudes in 23 of the world's biggest countries, covering almost 5 billion people.

The 2019 survey canvassed 25,325 people online across much of Europe, the Americas, Africa and Asia in February and March.

Questions about populist attitudes and convictions were inserted in order to derive a "populist cohort", and discover what this group of people think about major world issues from immigration to vaccination, social media and globalisation. The full methodology can be found here.

Analysis of the survey found the clearest tendency among people with strongly held populist attitudes was a belief in conspiracy theories that were contradicted by science or factual evidence.

The research may go some way towards understanding the success of rightwing populists such as Donald Trump and Jair Bolsonaro, who have fuelled conspiracy theories, undermined efforts to address global warming and dismissed fact-based journalism as “fake news”.

The survey findings may also prove useful to public health officials who are battling to contain outbreaks of measles around the world amid alarming rates of unvaccinated children.

The World Health Organization and other public health bodies have embarked on major campaigns to remind the public of the importance of vaccination as anti-vaccine propaganda and conspiracy theories have flourished on social media.

Unicef recently revealed that measles cases had risen 300% in the first three months of this year compared with the same time last year. In 2017, approximately 110,000 people died of the illness, most of them children. About 169 million children under 10 worldwide are unvaccinated, the UN agency said.

In the YouGov survey, people with strongly held populist views were on average almost twice as likely to believe that supposed harmful effects of vaccines were being deliberately hidden from the public. They were similarly more likely to believe that the US government knowingly helped the 9/11 terrorist attackers, and that manmade global warming was a hoax.

Two in five populists in the survey agreed that regardless of who was officially in charge of governments, “there is a single group of people who secretly control events and rule the world together”, compared with just under a quarter of the overall survey respondents.

The survey – of more than 25,000 people across almost two dozen countries – is the largest study of its kind undertaken by YouGov, and covers parts of Europe, the Americas, Africa and Asia. In total, the surveyed countries represent 4.7 billion people, or more than 60% of the world’s population. The Guardian helped design the survey, which will be repeated annually, and is exclusively releasing the findings.

Working with political scientists, the Guardian also identified a cohort of the survey respondents across 19 major democracies who held strongly populist views. They comprised 22% of global survey respondents, but their numbers varied significantly by country.

Brazil, where Bolsonaro was elected president last year, was the most populist country in the survey, with 42% of the population saying they strongly agreed with populist statements, followed by South Africa at 39%. Both countries have been rocked by a succession of corruption scandals in recent years.

One in four Americans belonged to the survey’s populist cohort – a similar proportion to Poland, France and Spain, the three most populist European countries in the survey. Considerably less populist were Canada, the UK and Sweden, where fewer than 15% of people had strongly populist views, and Japan and Denmark, where populists constituted less than 10% of the population.

The YouGov data was analysed by Matthijs Rooduijn and Levente Littvay, academics at the University of Amsterdam and the Central European University.

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The political scientists said there was reason to expect a close relationship between some conspiracy theories and populism – which typically involves a belief that amoral elites are in cahoots, exploiting ordinary people for their own self-interest. “But the strength of the association in this YouGov data, which covers a range of very different conspiracy theories across a diverse set of countries, is really quite remarkable,” they added.

The association was especially strong in the UK, where populists, in analysis that controlled for sociodemographic factors, were about three times as likely to believe in several conspiracy theories, including the idea that humans have made contact with aliens and this fact has been deliberately hidden from the public and that Aids has been spread around the world on purpose by a secret group or organisation.

Across all 19 nations that were analysed, the Guardian found people with strong populist views were also considerably more likely to subscribe to the view that their country’s political system was “broken” and in need of “total change”, and less trusting of national television news channels and broadsheet newspapers.

The populists were also more likely to say they consumed news on social media platforms including Facebook, Twitter, YouTube and WhatsApp, where conspiracy theories are known to flourish.

A further link between rightwing populism, in particular, and anti-vaccination theories was made by Jonathan Kennedy from Queen Mary University of London, who also analysed the YouGov data.

Reviewing the voting history of survey respondents in eight major European countries, Kennedy found 25% of those who had cast a ballot for rightwing populist candidates and parties had concerns about the effects of vaccines, compared with 14% of the rest of the population.

The difference between rightwing populist voters and others was largest in the UK, where a third of former Ukip voters had concerns about the harmful effects of vaccines – three times the proportion of Labour (10%) and Conservative voters (11%).

In France, which has the highest levels of vaccine hesitancy in the world, 44% of those who voted for Marine Le Pen in the 2017 presidential election expressed concerns about vaccines compared with 25% who did not vote and 12% of those who voted for Emmanuel Macron.

In Italy, supporters of the anti-establishment populist Five Star Movement, which has in the past promoted anti-vaccine propaganda, were more likely than voters of other major parties to doubt the scientific consensus. However, the finding did not hold for voters for Spain’s leftwing populist party, Podemos, who were less likely to believe in a vaccine conspiracy than voters of most other Spanish parties.

“This is a really exciting dataset because it allows us to start to understand what is driving individuals’ concerns about vaccines,” said Kennedy, who has published his own research exploring the relationship between populism and vaccines in the European Journal of Public Health.

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“The scientific consensus is that vaccines such as MMR are safe and produce massive benefits for human society – that they save several million lives each year,” he added.

“Why, then, does such a large proportion of the population not believe the scientific evidence? The data shows that this doesn’t seem to have much to do with factors like education, as we might expect. Instead, it is driven by anger and suspicion towards elites and experts that has also resulted in increasing support for anti-establishment political parties across Europe and beyond.”