The Guardian reports on a multi-national survey by the Ipsos Mori market research company, comparing people's perception of a number of national statistics with the actual statistics. There's also an interactive quiz which allows you to feel superior to your countrymen. Some of the findings:
(Score: 1) by tfried on Thursday December 03 2015, @05:16PM
Obesity is medically defined by being BMI 30+. That's objective, if not necessarily a perfect reflection of health.
True. But the likely issue underlying the systematic error is that people are mis-estimating the "level of fatness" that doctors consider overweight, not that they are systematically wrong at estimating, say, how many people are fatter than themselves.
"Wealth" is a legitimate gripe, but can be estimated through net worth.
Yes, but it's hard to put into a single figure. People might actually know some indicator like percentage of wealth owned by the poorest half of the population, or percentage of population owning half of the nations wealth, or ratio of wealth between top 1% and median, or percentage of wealth owned by top 10%, or... And the problem is, even if you know one or two of these indicators, you still don't have much of a basis for estimating an arbitrary other (such as the one the researchers asked for). (Also, in fact, I'd imagine the smaller the slice you are asking for, the higher the systematic error in estimates that you will find.)
Similar problems for estimating average age, or percentage of people below 14 years. Neither is likely to be an often cited statistic (contrary to, say, percentage people below voting age, or percentage people above typical retirement age). And even if you happen to have a pretty clear idea of the shape of your countries age pyramid, estimating either value in a few seconds is still a non-trivial exercise. Thus, no surprise to find people resorting to some sort of error-prone heuristic.