Census Summary Files Explained

Short Form vs. Long Form (2000 & Earlier Censuses)

How do you know where in the Census to find your variables? The Census files are organized by how the data was collected.

From 1940 to 2000, the Census Bureau used two forms to collect data. Use of the same questions to conduct the decennial Census is mandated by the Constitution; but it was impractical to gather much more than the basics in this way. The second form that was added contained many more questions but was sent to only a percentage of the population. Then estimates were statistically created from the data gathered with this form for the whole country. Statisticians argue that this is actually a more accurate way of providing information about the population because the statistics can be controlled to account for groups that are hard to count.

Summary Files 1 and 2 Summary Files 3 and 4
"Short Form" or 100%
"Long Form" or sample
Smallest Geography
block group
Variety of variables

The even-numbered summary files provide more detail about the immediately preceding file. So Summary File 2 gives more detail of Summary File 1 variables, and Summary File 4 gives more detail of Summary File 3 variables.

More specific descriptions of each file's content for the 2000 Census is available from the links below:

Summary File 1(This link is broken. We're working on fixing it) | Summary File 2(This link is broken. We're working on fixing it) | Summary File 3(This link is broken. We're working on fixing it) | Summary File 4(This link is broken. We're working on fixing it)

Decennial Census versus American Community Survey (ACS) (2010 and Forward)

Beginning in 2010, a long form is no longer part of the decennial census. Instead, the American Community Survey has taken it's place.  The ACS is administered every year, and provides much more current data for use by government at all levels, businesses, and the public at large. Its variables are similar to those of the decennial long form. Because the ACS is drastically different in methodology from decennial censuses up to 2000, comparing data with earlier years' long form data must be done cautiously.

Detailed comparison of decennial and ACS data