Birth location =/= mailing address zipcode. Babies are usually born in hospitals, and thus parents from many areas concentrate in one specific building. When you re-distribute these births out to their respective homes around the county, the zip code becomes much more important.
In towns like mine, however, 40,000 people share the same zip code with the hospital. I'm sure there are quite a few more town like mine throughout the US.
US pop in 2000: 280,000,000 —
US births in 2000: 4,000,000 —
US births per day: 10,958 —
Fraction of US pop that 40,000 represents: 0.0001428 —
Number of births per day for the 40,000: 1.56
That seems inline with the conclusion of the paper. See any mistakes?
