How the Census Works

Technology and the Census
The pantograph  machine allowed census workers to use punch cards for the first time in 1890.
The pantograph machine allowed census workers to use punch cards for the first time in 1890.
U.S. Census Bureau

Census taking became more streamlined in 1880 when trained workers were employed for the first time. Technology followed in 1890. The Census Bureau developed a new electrical machine that could add up responses to questions after census workers punched holes in the right places for each answer. Cards were then fed into a machine that totaled the result. It was bulky but a great advance at that time -- anything that sped up the process was a help since some of the results have to be ready nine months after Census Day (more about that later).

The first modern computer, called ENIAC, was invented in 1946 at the University of Pennsylvania. This computer, which was really many machines working together, took up a whole room. The system was ready in time for use in parts of the 1950 census, and the Census Bureau ordered its own computer, called UNIVAC. That technology has advanced over the years and now high-speed, supercomputers assist with the census.

The major technological leap for the 2010 census was the use of handheld GPS devices to update the Census Bureau's master address list of the nation's 145 million residences. The accuracy of GPS coordinates allowed the bureau to assign each home, apartment or trailer to its appropriate Congressional district. In the past, armed only with paper maps, census workers accidentally assigned an average of 5 percent of American residences — particularly rural homes — to the wrong district. With the upgrade to GPS devices, the bureau projected a 0.05 percent error rate [source: Luhby].

The Census Bureau uses the National Processing Center and works with contractors who operate three processing centers responsible for a variety of data capture functions:

  • A full electronic data capture and processing system records an image of every questionnaire.
  • Questionnaires returned by mail are sorted automatically to ensure timely capture of critical information needed before the non-response follow-up.
  • Optical mark recognition is used for all check-box data items.
  • Intelligent character recognition (ICR) is used to capture write-in character-based data items.
  • A clerical keying operation captures and resolves difficult ICR cases.
  • A quality assurance review is conducted on data keying and scanning activities.

Most of the U.S. census was taken door-to-door until 1960, when census officials recognized the inefficiency of this method in dealing with such a fast-growing, mobile population. That's when they decided to use the mail to distribute forms. In the 2010 census, 74 percent of households returned their census forms by mail, and the remaining households were counted by an army of census workers. The 1.4 million workers hired in 2009 and 2010 for the census included the following positions:

  • Administrators -- They determine how each division of the Census Bureau will do its part in the census.
  • Enumerators -- 585,000 workers went door-to-door in 2010 to gather information from residents who did not mail in their census forms.
  • Statisticians -- They make sure the Census Bureau's math is right.
  • Demographers -- These people understand the statistics and have studied what statistics tell about American life. They analyze the census numbers, comparing them with numbers from earlier censuses, and tell us important things about the future.

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