You are probably familiar with polling results showing "+/- 3 percentage points." The error gives you an idea about how confident you can be that your estimates are correct. Much like those ubiquitous polls, the ACS survey comes with error, too. Because the sample size is so much smaller than the regular Census, the margins of error are much greater. This workshop is too short to go into the finer details about standard error, but you should have some basic awareness about it.
What is standard error? The Census says "The standard error is a measure of the deviation of a sample estimate from the average of all possible samples."
Note: Social Explorer reports standard error, while American FactFinder reports Margin of Error. Margin of Error is a simple transformation of standard error. The Margin of Error reported in American FactFinder reflects a 90 percent margin of error. You can use the reported standard error in Social Explorer to create a Margin of Error.
Why would you care? If you are comparing estimates, for example comparing two counties within the same survey, or the same county across different survey years, you should conduct statistical testing to determine if the differences are statistically significant or not.
You can learn more about simple statistical tests for the ACS here:
Using the "American Community Survey: Accuracy" link (above), use the formulas located in the "Instructions for Applying Statistical Testing" to determine if the different categories in the "Educational Attainment for the Population 25 Years and Over" table for Albemarle and Loudon Counties are statistically different at the 90% level.
Using Social Explorer: