Where are all the immigrant stats. coming from?

http://www.cis.org/articles/2005/back1105.html

Steven A. Camarota- center of immigration studies.com

One would think that since Illegal immigrants are elusive and hiding from the government officials on account of their fear of deportation that they would be uncountable. However, it has been calculated in detail their activities through interesting, clever, and well devised methods that support the numbers in the data that gets published. They use the Census that is to be done by most of the population and then calculate from their data which ones of those that reponded where most likely to be illegal immigrants. We can rest assured that the stats. are well calculated.