It's TiVo, not Nielsen. TiVo has created a ratings system that includes demographic information beyond just sex and age. I'm not sure exactly how the determine party ID, as it's not specified in the piece. But, I'm assuming that the people who participate in the TiVo PowerWatch program, complete a questionnaire in the sign-up process.
As you can most likely tell....I don’t have TiVo either. I haven’t found anything on TV that is such a must. But that’s just my opinion.