Why Sample in the Census?
What they planned to do Normal effort Special effort Census divides the US into 7,000,000 blocks Tries to get everyone in every block Special effort Take 10,000 blocks (randomly selected) Do completely independent count Cross check the lists
Why? Capture-recapture designs Have 20 researchers (covering different regions) catch and tag fish in a lake. Say they get 40 in all. Say the next day they fish again. They catch 50 fish. 8 have tags (8 of the 40 original tags). How many fish are there in the lake? 50/(8/40) = 250 (second capture sample)/(recapture ratio)