Failure to Measure Undercount. Categories of people who are less than enthusiastic about revealing their whereabouts to the government include drug dealers, illegal immigrants, people who are wanted by the police, people who think they might be wanted by the police sometime in the future, people who are behind in their child support payments, people who are dodging bill collectors, and people who just do not trust the government. Those who were unwilling to be counted by the census are not likely to step forward a few months later when their neighborhood is singled out for a special visit by someone asking more questions for the government. While the census is a well-recognized effort that targets the entire population, people who distrust the government may feel that the survey is focusing specifically on them. They may therefore try even harder to avoid the survey.
Homeless people pose an even greater problem.
If the survey tried to count homeless people in July, it would not necessarily find them in the same location where they may have been counted in April. The survey therefore does not even attempt to count homeless people. False Identification of Undercount. Given the obvious inability of the survey to reach many of the people who are missed by the census, its results in 1990 were surprising. Even after some of the problems that had been found were corrected the following year, the total net undercount derived from the survey was very close to the level suggested by demographic analysis.