But there's a more practical reason as well. If The Powers That Be culled data from your cable box or DVR service, it would be raw data. "While it certainly can tell you what was watched when, it can't tell you what was watched when by whom," Seidman explained. "And, that's sort of the big deal with Nielsen is that they can tell you who in the household watched, whether they're male or female, how old they are, how much money they make, etc." And, for television advertisers (for whom this data are intended), those sorts of demographics are key. Nielsen even accounts for those households that do not possess a television (and yes, there are a few--I even know one or two of them).
"Nielsen projects a lot of things based on, you know, the make up of the population, how old people are, whether they own pets, whether they own trucks, whether they're going to be buying cars, whether they own their home, all that kind of stuff. So they project a universe estimate for the United States, and then they try to create a panel that basically mirrors the universe estimates that they projected. It is all done via what's called Nielsen People Meters, boxes that hook up to the sets and track who's watching what when. Those are in about 25,000 homes and probably represent roughly 50,000 people."
Within each household, Seidman explained, each family member has a code, which is entered when he or she begins watching a series. "I believe that something has to be entered every 30 minutes or it won't count," he noted. "So if you're watching CSI Miami at 10:00 p.m. on Sunday night and you fall asleep, some of your time spent sleeping will be credited, but sooner or later [the box] will stop. You won't be credited with watching CBS for eight hours if you fall asleep for eight hours."
I wondered (facetiously) if boring shows had an unfair advantage. The show gets credit for being watched if it lulls you to sleep. "I think the later the show is on perhaps the more important that becomes," Seidman suggested, which makes sense. You're much more likely to fall asleep the later it gets.
So what do all those ratings numbers mean to the series, the network and to fans? If you look at the ratings sheet (as you might find it in TV Guide or Entertainment Weekly--or on the TV by the Numbers Website), you might see a listing like this for House, M.D: 9.688 million viewers, 5.8/9 HH, 3.6/10 18-49.
Seidman took me through each of these statistics. "The first number, the 9.688 million, that's the average number of viewers who watch the full show. It's not the total number of people who watched some part of House. It's not even necessarily the total number of people who watched the whole show but skipped the commercials on their DVR that night. It is the total number of minutes spent viewing "House" divided by 60 and then converted into people. So it's the average audience that watched the whole hour. It's not the total audience that watched any part of the hour."