How do TV networks know what you are watching?

This is only partially about identity, but demonstrates a significant concern over how identities are evaluated.

We've all "lost" a television show to poor ratings. But how many of us actually know what ratings are and how they are accounted for?

Television ratings are determined by a company known as Nielsen Media Research (hence the Nielsen Ratings). This company conducts population samplings of households across the US to determine television ratings.

The Nielsen ratings generally rely on ~5,000 households. Now there are about 99 million households in the US, so the population sampling represents only a small percentage of the actual population.

When organizations announce that 36 million people watched American Idol (how sad) last night, it is really an extrapolation of those 5,000 households.

What this means: Nielsen TV ratings sampled 5,000 households, and found that 1810 households watched American Idol.

Using the rules of sampling and statistical analysis, Nielsen is able to report that 36 million homes were tuned to American Idol.