I don't think this is a duplicate of What causes systematic under- or over-estimation of general knowledge quantities?, as the accepted (and only) answer doesn't answer this question.

YouGovAmerica published these results, rounded to the nearest whole percent, from January 2022 to the question, "If you had to guess …":

True Estimate What percentage of American adults?
0% 20% Have a household income over \$1 million
1% 21% Are transgender
1% 26% Have a household income over \$500,000
1% 27% Are Muslim
1% 27% Are Native American
2% 30% Are Jewish
3% 30% Live in New York City
3% 30% Are gay or lesbian
3% 33% Are atheists
4% 29% Are bisexual
4% 36% Are members of a union
5% 30% Are vegan or vegetarian
6% 29% Are Asian
6% 40% Are a military veteran
9% 30% Live in Texas
11% 34% Are left-handed
12% 32% Live in California
12% 41% Are Black
12% 37% Have an advanced degree
14% 33% Are first-generation immigrants
17% 39% Are Hispanic
22% 41% Are Catholic
32% 54% Own a gun
33% 47% Have at least a college degree
34% 38% Have a household income over \$100,000
37% 45% Have a passport
42% 51% Are Democrats
42% 56% Are obese
47% 50% Are Republicans
51% 55% Are married
57% 58% Have at least one child
62% 61% Voted in the 2020 election
62% 50% Have a household income over \$50,000
64% 59% Are white
65% 49% Own a house
66% 59% Are fully vaccinated against COVID-19
67% 62% Have a pet
70% 58% Are Christian
77% 50% Have read a book in the past year
82% 62% Have a household income over $25,000
83% 68% Have a driver's license
85% 76% Own a smartphone
88% 59% Have flown on a plane
88% 66% Own a car
89% 65% Have at least a high school degree

Without exception, the small true answers were over-estimated, and the larger true answers were under-estimated, as can be seen by the blue line (estimates) being much more centralized and vertical than the red line (true values) in their graph:

Graph showing True and Estimate lines crossing near where they are equal.

What causes people to over-estimate small proportions and under-estimate large proportions?

It can't simply be the result of bias created by the media, as this moderation happens even when the results are blatantly impossible: the estimates based on non-overlapping racial categories add up to 225%.

Note that I'm not asking about anything related to the individual topics themselves, only about this observed moderating effect.

  • $\begingroup$ The 0% true percentage of millionaire US households can be quite easily misinterpreted to mean that YouGovAmerica is suggesting there are no US millionaire households. That is badly done in my mind, but hey-ho 🙂 $\endgroup$ Nov 20, 2022 at 7:56
  • $\begingroup$ @ChrisRogers says "YouGovAmerica is suggesting there are no US millionaire households". No, you are inferring that. What It does say is "rounded to the nearest percent". So 0% simply means less than ½%. But either way, 20% is very much larger, and that's the important idea to get from this. $\endgroup$ Nov 20, 2022 at 14:07
  • $\begingroup$ You inferred what I said. I inferred nothing. I was just pointing out how some could easily misinterpret the data if it is read in the wrong way. "can be quite easily misinterpreted to mean..." $\endgroup$ Nov 20, 2022 at 19:22
  • $\begingroup$ @ChrisRogers, given that the numbers are rounded to the nearest integer, how could say ".25%" be better presented? $\endgroup$ Nov 20, 2022 at 21:14
  • 1
    $\begingroup$ What sort of answer are you looking for? Psychological biases tend to be observations of behavior - they're not necessarily caused by anything besides "how our brains work". Something like en.wikipedia.org/wiki/Heuristic_(psychology) might also be relevant. $\endgroup$
    – Bryan Krause
    Nov 21, 2022 at 17:43


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