Each Census ACS estimate comes with a margin of error (see What do Margins of Error indicate?) which is the range over which there is a 90% probability that the actual value lies. So if the estimate is 90% ± 2%, you have a 90% probability that the actual value is between 88% and 92%. If the margin is ± .02%, then there is a 90% probability that the actual estimate is between 89.98 and 90.02 — which is very tight.

When there are only a few households contributing data, the margins might be large, even up to 100%.

**Large margins of error indicate that the estimate itself is pretty soft.**

In addition, for smaller communities or areas, there may be no valid estimate. These values will show up as “Not available (NA)” in tables and on maps.