How true is the census, anway?
There are people who either won't answer the door for census takers or won't answer any of the questions correctly. There are people who resided in the same place for more than thirty years and neither receive forms in the mail nor get visited by takers. There are whole neighborhoods that get skipped over by census takers, for fear of being robbed or worse. And, once the process stops, there are people who cook the figures to advance a political agenda. So, why bother?
If you want to pick THAT type out of a crowd, just look for the festering scabs on their elbows.