Updated June 05, 2012
While Census 2010 apparently resulted in one of the most accurate counts of the nation's total population since 1790, extensive pre-census outreach efforts failed to prevent some minority groups from being undercounted, according to estimates released in May 2012 by the U.S. Census Bureau.
Based on follow-up surveys, the Census Bureau reported that Census 2010 resulted in an overcount of only 36,000 people out of total population of over 308 million, an effective error rate of just 0.01%.
By comparison, the 2000 census resulted in a 0.49% overcount and the 1990 Census had a net undercount of 1.61% and the, according to the Census Bureau.
The Census Bureau said the 36,000 person overcount was due mainly to white persons who owned multiple homes being counted more than once.
What are Over and Undercounts?
An "overcount" is the number of persons counted in a census who were counted multiple times or should not have been counted at all. An "undercount" is the number of person who should have been counted in a census, but were not. A small overcount is considered preferable to an undercount and is more easily resolved.
"On this one evaluation -- the net undercount of the total population -- this was an outstanding census," Census Bureau Director Robert Groves said in a press release. "When this fact is added to prior positive evaluations, the American public can be proud of the 2010 Census their participation made possible."
Some Minorities Still Undercounted
More Work Remains
As in past census, however, the population of some minority groups continued to be undercounted. The Census Bureau estimates that 2.1% of the black population was not counted in the 2010 census, compared to 1.8% in the 2000 census. The 0.7% undercount of the Hispanic population in the 2000 census, then considered statistically insignificant, increased to 1.5% in the 2010 census.
The combined undercount of black and Hispanic minorities represents about 1.5 million people who went uncounted by the census.
Undercounts of Asian, Native Hawaiian and other Pacific Islander populations were estimated to have been 0.1% and 1.3% respectively and were not considered by the Census
Bureau to be statistically significant.
About 4.9% of American Indians and Native Alaskans living on reservations were missed by the 2010 census, while the estimated error rate for American Indians not living on reservations was virtually zero.
The combined undercount of minorities in Census 2010 was statistically the same as in the 2000 census, despite the Census Bureau's extensive and expensive minority outreach programs that added greatly to the 2010 census cost of $14.7 billion.
Also See: 2010 Census Comes in $1.6 Billion Under Budget, But…
"While the overall coverage of the census was exemplary, the traditional hard-to-count groups, like renters, were counted less well," Census Director Groves said. "Because ethnic and racial minorities disproportionately live in hard-to-count circumstances, they too were undercounted relative to the majority population."
"More work remains to address persistent causes of undercounting, such as poverty, mobility, language isolation, low levels of education, and general awareness of the survey," said Deputy U.S. Commerce Secretary Rebecca Blank in a press release. "As a nation, it is imperative that we work to address economic inequalities that impact those populations by promoting education, opportunities and jobs-particularly those in high-paying, high-quality science, technology, engineering and math fields."
Right, Wrong and Just Plain Missed
Along with its estimate of overall accuracy, the Census Bureau announced its estimates of what it calls the "components of coverage" in Census 2010: the number of people who were counted correctly, incorrectly and simply missed altogether.
For example, among the 300.7 million people who live in housing units, including apartments, the Census Bureau estimates that about 94.7% were counted correctly, while about 3.3% were counted incorrectly. Approximately 84.9% of those incorrectly counted were duplicate responses, while the rest were incorrectly counted for another reason, such as people who died before Census Day (April 1, 2010), who were born after Census Day or provided fictitious census responses.
The Census Bureau estimated that Census 2010 count omitted about 16.0 million people. The omissions included people simply missed in the census and people whose census records could not be verified in the post-enumeration survey because they did not answer enough of the questions. Of the 16.0 million omissions, the Census Bureau estimated that about 6.0 million were probably counted in the census but couldn't be verified in the post-census evaluation.
"We'll use these coverage estimates to build a better 2020 Census," Groves said. "The 2010 Census used a variety of operations to improve coverage of the population. We now have measures of their success, which will inform cost-quality tradeoff decisions for the 2020 Census."
Mail it Back or Get a Visit
As in previous censuses, most people who failed or refused to fill out and mail back their Census 2010 questionnaires got a personal visit from a census taker.
According to the Census Bureau, people who mailed back their census forms were more likely to have been counted correctly, compared to those counted by the door-to-door census takers. In addition, the earlier the mailed back responses were mailed, the more likely they were to be accurate and complete.
Also See: What the Census Spent to Get You to 'Mail It Back'
As you might expect, among people contacted by door-to-door census takers, actual members of the household provided more accurate census information than "proxies," such as neighbors or landlords who were contacted when a householder could not be reached or refused to participate in the census.
Also See: Census Answers are Required by Law