[ajross]

Apportionment is based on direct census count only. Indeed there is better science available for population estimation (and IIRC some of it indeed gets done by the Census Bureau's reporting), but that's not how the law was written.

[thechao]

It's called the "American Community Survey" (https://en.wikipedia.org/wiki/American_Community_Survey). It's a great piece of high-quality, modern, scientifically valid demographic work that the C.B. does between its enforced stints with 18th c. `demographicology' that the constitution requires.