Ever since William the Conqueror compiled the Domesday Book in eleventh century England, census officals have had to face the fact that they cannot possibly include everyone in a national roll call. The problem has continued through the ages up to today, as current government people-counters realize that the U.S. Census Bureau's decennial national head-count is in no way completely accurate.
But a method developed recently by members of the Harvard Statistics Department may make the American census, in which officials estimate more than 1.4 percent of the 1980 population was either most or undercounted, a more exact process, and in doing so, these researchers may affect the way congressional disticts are determined and the process by which federal funds for social services are allocated.
"It builds on the idea of the capture-recapture" statistical technique, Donald B. Rubin, chairman of the Statistics Department, says of his census modification technique. Rubin explains the new procedure as similar to the method biology researchers use to study bird and animal populations. "It's like tagging fish in a pond, releasing them, and catching them again to see how the population has changed," he says.
Members of the Statistics Department, who have been working on this project for more than a year, propose selecting population segments of 300,000 homes in various regions across the country and then intensively studying their group dynamics after a normal U.S. census is taken by mail, said Rubin, who has been at Harvard for four years. The scientists, who include Rubin, Assistant Professor of Statistics Hal Stern and four graduate students, then use the results from these segmented studies to adjust the census' total population count.
"We would take the information from the census, which people mail in regarding numbers [of persons living] in houses, and would then send people to the same houses to take a new, more exact count. Then we would compare the two counts and arrive at a different adjustment factor for each population block--such as Black males or white, elderly women. By applying those numbers to national statistics, we would adjust for the names missed in the national mailing," says Rubin, who has worked with the Census Bureau on statistical problems several times over the last 10 years.
Currently, the U.S. holds a census every 10 years in which most of the people-counting is done by mail, according to Tom Belian, a graduate student working with Rubin on the project. Every American household receives a census form, which reports the number of people living at their home. "It's a huge undertaking, costing over $1 billion," Belian said. The Census Bureau has never before adjusted its population data.
Unfortunately, Rubin admits, solving the undercount problem involves more than just locating lazy census respondents. He says that the Department of Commerce realizes it misses those people who intentionally misrepresent the number of people in their households on their reports, as well as those who do not mail in any census forms at all.
"A lot of times people who live in overcrowded apartments, where there are limits on the number of residents, will say there are fewer people in their households because they think somehow Uncle Sam will notify their landlords and get them thrown out," Rubin says. "Sometimes women will also omit their husbabnds' names from the census because they think they will get more welfare money to take care of their children."
Rubin says evasive tactics such as the above examples skew population data, particularly those pertaining to minorities. Officials estimate that six percent of all Blacks were under-counted in the 1980 census, but that only 0.5 percent of all whites were missed. Rubin estimates that the census is losing track of more than 15 percent of Black males in some areas.
"We know [the uncounted citizens] are born and that they go to school, but after that they disappear for about 20 years and resurface in census counts much later," says the Princeton graduate.
Rubin says that estimating the exact number of people missed in a census is important to government and social service officials for two reasons. "One has to do with money, and the other has to do with legislation in Congress," he says.
If a city's population is undercounted, the federal government will not give the metropolis enough money to provide various services for all of its residents.
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