What the heck does the second census question mean?
The first asks you how many people are living at your house (but don’t count college students or people in jail, because they’ll be counted separately).
The second question asks how many people are living at your house that you didn’t count in the first question. What the heck?
My line of work involves a lot of public surveys, and what I hear from the people in the field is that respondents frequently give wrong or incomplete answers to what seem like very simple questions. Often, it’s because they’re either expecting a different question, or because the question doesn’t make sense to them, so they figure it must mean something else.
So for example, when people hear “How many people live here?” a lot of them automatically just count the people in their family: “There’s four: me, my spouse, and our two kids. Oh, but I see we don’t count kids in college. Huh, I guess it’s actually just three then. That’s strange.” But they forget that they have a boarder in their basement apartment, or they figure he should probably be counted separately, too. Or maybe their children have long since moved out, so they’re used to there being just two people living there. But one child lost her job and moved back home a few months ago, and has no other permanent residence. It’s easy to forget that, even though she’s been living on her own for decades, and probably will be moving out shortly, she’s technically living there now.
So they ask multiple times, in different ways, to make sure everyone is being counted.
They need to know how many of the people living in your house need to be otherwise accounted for that weren’t accounted for in Question 1. It seems pretty straightforward to me.
Yes, but the first question defines “living at your house” to not include students, jailbirds, etc.
So the second question, how many people are living at your house, should get the exact same answer as the first.
Maybe they want to get a separate count for the students and jailbirds.
My first thought is that the second question is looking for the students and prisoners that were excluded from the first question. Otherwise, the answer to the second question should always be zero, unless you’re one of those described by Heart of Dorkness who distinguishes between people living at your house and people living at your house. 
Seems to me the answer to the second question is zero (not the same answer as question 1) if you’ve answered question 1 correctly. The only thing that gave me pause in the first question was the April 1, 2010 date. Since this is still March, don’t we have to wait until April 1 to fill out the form? Anyhow, I’ve filled it out in less than 5 minutes and dropped it in the mailbox the next day.
No, because it’s specifically asking for those NOT counted in the first.
It appears to me that they are expecting the answer to question 2 to be zero, and that they ask it to get you to think a little harder about question 1. It also appears that they want to make sure you are excluding the people who are supposed to be excluded.
Just for the sake of accuracy, here are the questions and explanations.
This was my thought, too. The purpose of the second question is to catch incorrect responses to Q1 from stupid people (and people are stupid).
According to the Census Bureau,
For most people, this indeed means that the count in Question 2 should be zero. However, I’d like to point out that questions 1 and 2 are different; Q1 asks “How many people were living or staying…?” but Q2 asks “Were there any additional people staying here…?” Q1 is specifically limited to the definition that precedes it, but Q2 is not. In this category I might have listed the old college buddy who’s sleeping on the couch for a few weeks while he looks for a new apartment, or the children who do not live with me but are staying here while a new foster home is found. Any answer to Q2, in my opinion, alerts the bureau that a judgment call must be made.
Doesn’t the first question ask about an “address”?
OP and most respondents speak of “house”.
I thought the question would be easy to find but so far I have failed.
All of your census filling instructions are answered here:
http://www.hulu.com/watch/4165/saturday-night-live-census-taker
Try looking above in post #9. 