[USA] Homeward Bound: Recent Immigration Enforcement and the Decline in the Illegal Alien Population / Center for Immigration Studies, July 2008
PDF - http://www.cis.org/articles/2008/back808.pdf
"Monthly data collected by the Census Bureau through May 2008 shows a significant decline in the number of less-educated, young Hispanic immigrants in the country. The evidence indicates that the illegal immigrant population may have declined by over one million in the last year. There are strong indications immigration enforcement is responsible for at least part of the decline. The economy also is likely playing a role."