I didn’t!  

Ipsos MORI, a market research company, measured the distance peoples’ perceptions stray from reality. Americans scored worst – that is, the scores of Americans showed the largest gap between reality and perception – in a survey of fourteen industrialized countries. Italians are at the bottom with the US. Swedes and Germans ranked highest, although the report says even these two countries’ participating citizens are consistently wrong on some things.

Immigration and teenage pregnancies are two areas where Americans’ perception doesn’t match reality.  

Levels of immigration – a hot-button topic in many developed countries – are overestimated everywhere, but the United States veers further from reality than most, with an average guess that 32 percent of the population are immigrants when the reality is 13 percent.  

[…]Americans think 24 percent of girls aged 15 to 19 give birth each year, when the real figure is just 3 percent, and even the sensible Swedes are badly out, believing the annual teenage pregnancy rate is 8 percent compared to the actual 0.7 percent.

As with all surveys and measures of this sort there are plenty of questions over interpreting the meaning of what is shown by the results. And Bobby Duffy, global director of the Ipsos Social Research Institute wonders if people may be sending a message about what is worrying them as much as trying to reply to the questions correctly. But he warns

"Cause and effect can run both ways, with our concern leading to our misperceptions as much as our misperceptions creating our concern,"

The Ipsos MORI Perils of Perception Quiz can be taken here.  Test your own perception depth.