Census
A sample survey looks at only a part of the population. Why not look at the entire population? A census tries to do this.
Census
A census is a sample survey that attempts to include the entire population in the sample.
The U.S. Constitution requires a census of the American population every 10 years. A census of so large a population is expensive and takes a long time. Even the federal government, which can afford a census, uses samples such as the Current Population Survey to produce timely data on employment and many other variables. If the government asked every adult in the country about his or her employment, this month’s unemployment rate would be available next year rather than next month. In fact, to save money, the 2010 census consisted of only 10 questions. Five of these were general questions, and five required answers for every person living at the address the form was sent to.
Statistics in Your World
Is a census old fashioned?
The United States has taken a census every 10 years since 1790. Technology marches on, however, and replacements for a national census look promising. Denmark has no census, and France plans to eliminate its census. Denmark has a national register of all its residents, who carry identification cards and change their register entry whenever they move. France will replace its census by a large sample survey that rotates among the nation’s regions. The U.S. Census Bureau has a similar idea: the American Community Survey has already started and has eliminated the census “long form.” Canada has eliminated its long-form census and replaced it with a controversial voluntary National Household Survey.
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So time and money favor samples over a census. Samples can have other advantages as well. If you are testing fireworks or fuses, the sampled items are destroyed. Moreover, a sample can produce more accurate data than a census. A careful sample of an inventory of spare parts will almost certainly give more accurate results than asking the clerks to count all 500,000 parts in the warehouse. Bored people do not count accurately.
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The experience of the Census Bureau reminds us that a census can only attempt to sample the entire population. The bureau estimated that the 2010 census overcounted the American population by 0.01% but undercounted the black population by 2.1%. A census is not foolproof, even with the resources of the government behind it. Why take a census at all? The government needs block-by-block population figures to create election districts with equal populations. The main function of the U.S. census is to provide this local information.