Mr. David I don't think these numbers are quite accurate. Houston, as a sanctuary city, has probably a million or more undocumented immigrants. These people are not included in most statistics. By far and large, Houston is now a Hispanic City. Houston is the only place I know of in Texas that I can go to Burger King or Wendy's for a hamburger and be told no habla English
First, this is a radio board. So what we look at are radio markets, not cities. The Houston market is made up of 11 counties, not the city of Houston. Each county is weighted proportionally in Nielsen and sampled proportionally, too. Cities and townships are not specifically sampled as ratings are based on an economic boundary, not a political one.
Also note that the Census and OMB definition of the Houston metro is different than the radio one: Metro Survey Area vs. Metropolitan Statistical Area.
The Census and the annual revisions include the undocumented. Since the Census form does not have any place to indicated legal status, there is no official tally of that. The city of Houston, at around 2.2 million, is only around 30% of the market population.
Nielsen does not use Census numbers directly. They use independent demographers to do annual updates, and that data is based both on the Census and other indicators like car registrations, utility connections, etc. Nielsen revises the data annually.
In any case, illegal immigrants are very unlikely to participate in the Nielsen PPM process as doing so requires being tracked 24/7 and registering one's residence and phone number along with the rest of the household.