When it comes to estimating the size of demographic groups, Americans rarely get it right. In two recent YouGov polls, we asked respondents to guess the percentage (ranging from 0% to 100%) of American adults who are members of 43 different groups, including racial and religious groups, as well as other less frequently studied groups, such as pet owners and those who are left-handed.

When people’s average perceptions of group sizes are compared to actual population estimates, an intriguing pattern emerges: Americans tend to vastly overestimate the size of minority groups. This holds for sexual minorities, including the proportion of gays and lesbians (estimate: 30%, true: 3%), bisexuals (estimate: 29%, true: 4%), and people who are transgender (estimate: 21%, true: 0.6%).

It also applies to religious minorities, such as Muslim Americans (estimate: 27%, true: 1%) and Jewish Americans (estimate: 30%, true: 2%). And we find the same sorts of overestimates for racial and ethnic minorities, such as Native Americans (estimate: 27%, true: 1%), Asian Americans (estimate: 29%, true: 6%), and Black Americans (estimate: 41%, true: 12%).

A parallel pattern emerges when we look at estimates of majority groups: People tend to underestimate rather than overestimate their size relative to their actual share of the adult population. For instance, we find that people underestimate the proportion of American adults who are Christian (estimate: 58%, true: 70%) and the proportion who have at least a high school degree (estimate: 65%, true: 89%).

The most accurate estimates involved groups whose real proportion fell right around 50%, including the percentage of American adults who are married (estimate: 55%, true: 51%) and have at least one child (estimate: 58%, true: 57%).

Misperceptions of the size of minority groups have been identified in prior surveys, which observers have often attributed to social causes: fear of out-groups, lack of personal exposure, or portrayals in the media. Yet consistent with prior research, we find that the tendency to misestimate the size of demographic groups is actually one instance of a broader tendency to overestimate small proportions and underestimate large ones, regardless of the topic.

If exaggerated perceptions of minority groups’ share of the American population are due to fear, we would expect estimates of those groups’ share that are made by the groups’ members to be more accurate than those made by others. We tested this theory on minority groups that were represented by at least 100 respondents within our sample and found that they were no better (and often worse) than non-group members at guessing the relative size of the minority group they belong to.

Black Americans estimate that, on average, Black people make up 52% of the U.S. adult population; non-Black Americans estimate the proportion is roughly 39%, closer to the real figure of 12%. First-generation immigrants we surveyed estimate that first-generation immigrants account for 40% of U.S. adults, while non-immigrants guess it is around 31%, closer to the actual figure of 14%.

Although there is some question-by-question variability, the results from our survey show that inaccurate perceptions of group size are not limited to the types of socially charged group divisions typically explored in similar studies: race, religion, sexuality, education, and income. Americans are equally likely to misestimate the size of less widely discussed groups, such as adults who are left-handed. While respondents estimated that 34% of U.S. adults are left-handed, the real estimate lies closer to 10-12%. Similar misperceptions are found regarding the proportion of American adults who own a pet, have read a book in the past year, or reside in various cities or states. This suggests that errors in judgment are not due to the specific context surrounding a certain group.

Why is demographic math so difficult? One recent meta-study suggests that when people are asked to make an estimation they are uncertain about, such as the size of a population, they tend to rescale their perceptions in a rational manner. When a person’s lived experience suggests an extreme value — such as a small proportion of people who are Jewish or a large proportion of people who are Christian — they often assume, reasonably, that their experiences are biased. In response, they adjust their prior estimate of a group’s size accordingly by shifting it closer to what they perceive to be the mean group size (that is, 50%). This can facilitate misestimation in surveys, such as ours, which don’t require people to make tradeoffs by constraining the sum of group proportions within a certain category to 100%.

This reasoning process — referred to as uncertainty-based rescaling — leads people to systematically overestimate the size of small values and underestimate the size of large values. It also explains why estimates of populations closer to 0% (e.g., LGBT people, Muslims, and Native Americans) and populations closer to 100% (e.g., adults with a high school degree or who own a car) are less accurate than estimates of populations that are closer to 50%, such as the percentage of American adults who are married or have a child.

Does correcting misperceptions of group size change peoples’ attitudes on related issues? Current research suggests it does not. In a series of studies (one of which used a survey fielded by YouGov), political scientists John Sides and Jack Citrin attempted to correct inaccurate beliefs about the size of the U.S. foreign-born population, both subtly, by embedding the accurate information in a news story, and explicitly, by providing survey respondents with Census Bureau estimates. They found that while providing this information did somewhat improve people’s knowledge of the number of immigrants in America, they did not make people more supportive of immigration.

Below we display median estimates of group sizes, which tended to be more accurate than mean estimates, but with differences from the true estimates in the same direction.

Methodology: This article includes findings from two U.S. News surveys conducted by YouGov on two nationally representative samples of 1,000 U.S. adult citizens interviewed online from January 14-20, 2022. The first survey included questions on groups involving race, education, income, family, gender, and sexuality, while the second survey included questions on religion, politics, and other miscellaneous groups. The samples were weighted according to gender, age, race, and education based on the 2018 American Community Survey, conducted by the U.S. Census Bureau, as well as 2016 and 2020 Presidential votes (or non-votes). Respondents were selected from YouGov’s opt-in panel to be representative of all U.S. citizens. Real proportions were taken from a variety of sources, including the U.S. Census Bureau, the Bureau of Labor Statistics, YouGov’s internal poll results, and the results of other well-established polling firms. Most estimates were collected within the past three years; the oldest is from 2009. Because the real estimates presented cover a range of time periods, they may differ from actual population sizes at the time our survey was conducted.