The files are also available on the Census FTP site including text versions of the In-, Out-, Net, and Gross Migration files.
Sample size and data quality measures (including coverage rates, allocation rates, and response rates) can be found on the American Community Survey website in the Methodology section.
Data are based on a sample and are subject to sampling variability. The degree of uncertainty for an estimate arising from sampling variability is represented through the use of a margin of error. The value shown here is the 90 percent margin of error. The margin of error can be interpreted roughly as providing a 90 percent probability that the interval defined by the estimate minus the margin of error and the estimate plus the margin of error (the lower and upper confidence bounds) contains the true value. In addition to sampling variability, the ACS estimates are subject to nonsampling error (for a discussion of nonsampling variability, see Accuracy of the Data). The effect of nonsampling error is not represented in these tables.
Hurricanes caused a disruption of data collection activities from September through December of 2017 in Puerto Rico. All 2017 1-year estimates for Puerto Rico are based on data collected prior to this disruption. For more information, see https://www.census.gov/programs-surveys/acs/technical-documentation/user-notes/2018-02.html.