What would happen to the American Community Survey (ACS) if it was not mandated by law? The Census Bureau has looked at this question, and our research shows that a voluntary survey would reduce the self-response rates significantly. To make up the shortfall, we would have to increase the number of households surveyed and conduct much more in-person follow-up, at an additional cost of more than $90 million annually. If we were not able to increase the number of households surveyed, we would collect much less data and accuracy would decrease due to increased sampling variation. This would disproportionately affect the accuracy of the results that we produce for many small areas and small population groups throughout the nation.

The two maps below show the percentages of census tracts within each county with acceptable quality data. The first map shows the percentages under the current, mandatory approach. As a mandatory survey, a small percentage of counties in off-white (about five percent) have less than 20 percent of their tracts with acceptable quality data. This impacts about 2.5 million people.

The second map shows that as a voluntary survey (with the reductions in sample size, assuming that the budget stays fixed), the number of people increases to 62.9 million. That is, 62.9 million people live in counties where less than 20 percent of their tracts have acceptable quality data, representing about 26 percent of counties. This is represented as off-white on the map below.

You can also download the complete set of maps [PDF - 3.3 MB] or download the companion spreadsheet [XLS - 350 KB] for the nation, states, and District of Columbia showing the percentage of census tracts within each county that have acceptable levels of quality data.