Lt. Governor Dewhurst was trying to make the point--using round numbers--that roughly half of the total population growth in Texas is from migration; the other half is due to natural increases. 

Total Population Change 2009 = 478,012 (roughly 500,000)
Total Migration 2009 = 231,539 (roughly 250,000)
Total Natural Increase 2009 = 245,537 (roughly 250,000)

Mike Walz
Communications Director
Office of Lt. Governor David Dewhurst