The Numbers Guy’s blog post, The Census’s 21st-Century Challenges, discusses the difficulty with conducting a nation wide survey. Part of the challenge lies in getting the survey to the people. Some people do not have a permanent address, or have moved recently without their address being updated. Another problem lies in actually getting those who receive the survey to participate.

The U.S. census claims to be mandatory, but lacks the enforcement to be so. That’s not to say that calling it mandatory is useless. It’s estimated that by replacing the word “voluntary” with “mandatory” increased survey response by about 20%.