Source File: http://www.census.gov/popest/data/intercensal/national/files/US-EST90INT-07.csv
File Layout: http://www.census.gov/popest/data/intercensal/national/files/US_INT90.txt
Source URL: http://www.census.gov/popest/data/intercensal/national/index.html
usint set up by Jean Roth , jroth@nber.org , 18 Oct 2016