About the 2005 American Community Survey

The ACS is about characteristics of the population, not the size. If you are looking forward to getting new and improved data regarding the number of Hispanics (or African Americans, or foreign born persons, or poor persons, etc.) living in your state or metropolitan area, or city or county don't get your hopes up. The ACS does not provide any new data regarding the counts of persons or households. This is because the Census Bureau does not weight ACS survey returns the way they do with decennial census surveys. In the decennial census, the Bureau assigns weights based upon their master address list which is assumed to be definitive and complete.

Master Address File

This is not the case with the MAF (Master Address File) used for the ACS. While an initial weight may be assigned based on the number of households found in an area on the MAF, the person record weights are adjusted so that total population counts at the county level by certain age, race, gender and Hispanic cohorts will match numbers published in the Bureau's detailed county-level demographic estimates.

The result is that the number of cases (persons) in a table is really just a reflection of those estimates, and the data collected in the ACS simply controls the apportioning of those cases (total persons in households, households with Hispanic head, total males living in households, etc.) based on characteristics. So the ACS may tell us what portion of African Americans are classified as living in poverty in a county, but the actual number of such persons is the result of applying that portion to the number of African Americans that are estimated (some would say "guesstimated") in the Bureau's estimates program.

Source

Information from the Missouri State Data Center.