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Oct 5, 2009 11:22 pm US/Central
Good Question: How Do TV Ratings Work?
(WCCO)
Every week, there's a new list of the top 10 television programs, listing the total audience for each show. But how does anyone really know how many of us are watching television?
"How do TV news organizations know what their viewership is on a given day? How can they tell who is watching what on TV?" e-mailed Kathryn Engel, in Minnetrista.
"Well, Nielsen tells us everything," said Shannan Cranbrook, Broadcast Director for Minneapolis ad agency Periscope. Cranbrook helps clients negotiate prices for ad time at television stations and networks.
The Nielsen Company is a large corporation which specializes in audience measurement and then sells that data to ad agencies and television stations.
So how do they know who's watching?
"They pick a sampling of the U.S. to put meters in their homes," said Cranbrook.
In the Minneapolis-St. Paul viewing area, there are 1.7 million television households. Only 610 of those homes have meters installed. Local people meters are devices hooked to a television set. People in the household have to log-on by pushing a button, so Nielsen knows who is watching a certain program.
Those 610 meters represent about 1,200 people, age 2 and older.
That sample is statistically valid, using people from various age, race and economic backgrounds to make up a sample that's representative of the total population.
"That information gets downloaded every night and then they're able to look at that sample and project it to the total U.S., or the total Minneapolis market. And tell you, '13 million watched 'Desperate Housewives' last night,' but really that's only based on a couple of thousand set-top boxes," said Cranbrook.
The sample can be carved up into demographics. Advertisers care most about viewers who are 25 to 54 years old.
"They're going to be your largest consumer," she explained.
The audience measurement system isn't perfect, said Cranbrook, but "it's the best system we have."
It's also the only system. There is no major competitor to Nielsen, although the major television networks are talking about starting up their own audience measurement system.
The ratings are essentially the "currency" of the television business.
"That's what people will pay you based on. Because you're not going to be able to tell anybody, for sure, exactly how many people watched," explained Cranbrook.
In some parts of the country, there are no people meters. In Duluth and Rochester, viewers have to send in hand-written diaries, recording what shows they watched. According to Nielsen, the company processes 1.6 million diaries each year. Those diaries are collected four times a year, in periods referred to as "sweeps."
(© MMIX, CBS Broadcasting Inc. All Rights Reserved.)
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