Inequality, immigration, obesity. People hold strong views about these thorny public challenges. It’s a shame, then, that most don’t know even basic facts about them.

Polling firm Ipsos MORI published its latest “Perils of Perception” report today (Dec. 2), and it makes for uncomfortable reading. The company surveyed people about the demographics of their countries. “Across all 33 countries in the study, each population gets a lot wrong,” said Bobby Duffy, managing director of the Ipsos MORI Social Research Institute. “We over-estimate what we worry about.”

Those polled think that one in four people around them is an immigrant, for example, when the real figure is fewer than one in 10. Argentinians are way, way off—they reckon that 30% of people in the country are immigrants, when in reality the share is just 5%.

When it comes to inequality, people in the survey globally think the richest 1% own nearly half of all wealth in their country, when the actual figure is closer to a third. This seems a particular worry among Brits, who were off by the most—reckoning that plutocrats’ share is more than twice the actual average (59% versus 23%).

Aging is another issue that people tend to overestimate. Across the survey, people thought the average age in their country is 50 years old, versus the actual of 37. Brazilians were particularly bad at judging this, saying that the average age of people in their country is 56 when it is actually 31.

By contrast, obesity is an issue that the people in Ipsos’s survey appear to underestimate. The average guess for the share of overweight or obese people is 40%, versus an actual figure of 54%. Saudis, for example, think that just over a quarter of their country is overweight, when in reality the figure is around 70%.

Adding this all up, the pollster came up with a ranking it rather coarsely dubs the “Index of Ignorance.” This year’s “winner” is Mexico, taking that dubious honor from last year’s title holder, Italy.