Resolved Question

They put electrical monitoring boxes on top of a few people's TVs, and these send viewing information back to the polling company. These boxes will often require an individual pin number for each viewer as well, so that they can identify the age and gender of who is actually watching the show. Don't worry, they always ask those families first - it's a voluntary survey. They try to ensure that they get a statistical cross-section of the country (age, financial status, ethnic group, etc), and then extrapolate that information outwards. (for instance, if you were surveying 100 TVs, and 40 of them were tuned to the same program, then they could safely say that roughly 40% of the country's population was watching that show at that time). It can be a bit of an inexact science, however, so if I were you I'd always take those viewing statistics you hear with a grain of salt!