Ok, so I just got a phone poll call...

They asked "Are you registered to vote" and then "age" .... After I told them my age group, they said "Thanks, we have enough people in your category" and hung up.

SOOOO .... question for someone maybe in the polling business or more informed ...

HOW does that work? Before the poll they decide "we want 100 people from ages 45 to 54, and no more"? Doesn't that sort of bias the poll? If they get more from one group who are willing to answer, shouldn't "random sampling" make you take those? How do they decide that "first" 100 (or whatever) of a age group are the "right" 100?

This is not meant to be a "polls are all wrong" question ... more a statistics and polling mechanics question because I'm kind of a nerdy guy in that way and I'm curious....