[jg42]

I can't get the math to work to reach 475 million American adults.

Our current population is only 347 million and the birthrate is about 1.25%. Running a total for the last 20 years or so I can't get more than 300 million adults or so.

Any math folks that want to analyze the number of unique adults entering/leaving the US from 1990 to 2011?

[spicymaki]

I think idea is the sample size of 60k was varied enough to represent a population size of up to 475M. More than enough to reflect the real population and then some.