Census Summary Files
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.
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:
Beginning in 2010, a long form is no longer part of the decennial census. Instead, a whole new survey has taken its place. The good news is that the new instrument, the American Community Survey, will be administered every year, providing much more current data for use by government at all levels, businesses, and the public at large. Its variables will be similar to those of the decennial long form. The bad news is that the ACS is a completely new survey. Because it is drastically different in methodology from the decennial census, comparing data with earlier years' long form data must be done cautiously.