Actually, a representative sample doesn’t have to be very large to represent the population it is drawn from. For example, you don’t need to eat an entire pot of vegetable soup to know what kind of soup it is. A cup of soup is more than adequate to represent what is in the pot. If, however, you don’t stir the soup to make sure that all of the various ingredients have a good chance of ending up in the cup, you might just pour a cup of vegetable broth. Stirring the soup is a way to make sure that the sample you draw represents all the different parts of what is in the pot.
While a sample doesn’t have to be very large to represent the population, the sample does need to be selected in a way which gives all members of the population the same chance of being chosen.
The way that Nielsen Media Research finds out about who is watching is to measure what a sample of television viewers are watching. For our national ratings estimates, Nielsen Media Research uses a sample of more than 5,000 households, containing over 13,000 people who have agreed to participate. Since there are over 99 million households with TVs in the U.S., it might seem that a sample of 5,000 is just not big enough to represent the nation.
If we wanted a closer estimate, we would take a larger sample. Imagine if we stirred well and then poured out enough soup to contain 5,000 vegetable pieces. We probably wouldn’t get exactly 2,500 carrot pieces, but the chance of getting no carrots at all is very remote. In fact, according to sampling theory and a very tasty laboratory test, 19 out of 20 times we take a well-stirred sample of soup containing 5,000 vegetable pieces, we get between 48% and 52% carrots. There is no guarantee that the percentage of carrots in a sample of this size will be between 48% and 52% (one time in 20 it will be outside this range, but usually not far outside this range). The same sampling errors apply to a representative sample of television viewers.
How does this work? What is being researched?
Measuring TV sets :
In a specially selected sample of homes, Nielsen Media Research technicians install metering equipment on TV sets, VCRs and cable boxes (and even satellite dishes). The NielsenTV meters automatically and invisibly keep track of when the sets are on and what the sets are tuned to. These meters are connected to a central “black box,” which is actually a very small computer and modem. Information from the meters is collected by the black box, and in the middle of the night all the black boxes call in their information to our central computers.
Identifying TV programs :
Nielsen Media Research’s primary source of information about which programs are airing for each station or cable channel comes from a very special coded ID number that is part of almost every TV picture-a series of lines and dots in the top edge of the picture which labels the program and episode. Nielsen Media Research developed and patented this systems, which we call AMOL, or Automated Measurement Of Line-ups. All across the country, we have sites where TV stations are monitored and the program ID codes are detected and collected. Each night, these monitoring sites connect up to our central computer and download the information. We compile the electronic program information and compare it to other sources of information we have already received. If there are discrepancies, we call TV stations and cable operators to verify what actually was aired. Keeping track of what is on TV is also done with the help of program listings provided by networks, stations and cable systems, as well as published TV listings.
Identifying commercials :
Although there are many TV programs, there are even more commercials. Keeping track of what commercials are on TV is another service provided by Nielsen Media Research. Using a special passive TV signal identification technology, commercials on TV stations are continuously monitored and converted into a digital “fingerprint”. These fingerprints are then compared to a computer file of fingerprints from thousands of different commercials and automatically identified whenever possible (which is about 95% of the time). The other 5% of the time, videotapes of unmatched commercials are sent to a central office to be viewed and properly credited. This information is used to produce reports detailing when and where TV commercials actually aired.
Measuring people :
This is the main ingredient in the recipe for ratings: who is watching? When Nielsen Media Research combines the measurement of who is watching with what channel is tuned and what program is on that channel, Nielsen Media Research can credit viewing to a program.
In their national sample, Nielsen Media Research installs set meters which have an attachment called a “People Meter“. The People Meter is a box, about the size of a paperback book, which is placed on or near each TV set.
The box has buttons and lights which are assigned to each person who lives in the household (with additional buttons for guests). There is also a remote control to operate the people meter from anywhere in the room. When a viewer begins watching TV, they push their button, changing their indicator light from red to green. When they finish watching, they push their button again and the indicator changes back to red.
Periodically, the lights flash to remind people to check to make sure that the information in the people meter is accurate. Information from the people meters is combined with set tuning information and relayed to Nielsen Media Research each night.
All the text in this post comes from the Nielsen Media Research website.
It’s posted here because I’ve got to replicate it in about seven hours in front of my professor at school. Now I can have a quick peek to the main points from the very long essay about viewer research, before I go to school. This is not intended to be advertisement for Nielsen Media Research, and I claim no rights at all. I just needed the words. :)