Question: If the Census is confidential and not meant to gather "personal" information, why does it ask for your phone number?
Answer, courtesy of Dr. Groves' Census blog:
"We found over past censuses that sometimes there are contradictory answers given on some questions. For example, some folks in the first question on the form answer that there are four people living in the household. Then, as they proceed through the form, they report the attributes of only three people. This is easy to do if you lose track of your progress through the form. When we process the form in our centers, we notice this discrepancy. We are devoted to making sure we collect the most accurate data possible.
With the telephone number of the household we can have a quick telephone call to resolve the discrepancy. Our only use of the telephone number is to verify that we have recorded accurate information about the household.
Like all census responses, the telephone number is shared with no other agency or company. Once we make sure we understand all your responses, we remove the record of the telephone number from our files."