frequently asked questions about nielsen ratings
(last updated: thursday, august 23, 2007)

Every so often we like to revisit our frequently asked questions about Nielsen Ratings. Here's the latest update:

1. In your daily ratings breakdown, I always see the following information: "My Name Is Earl" (households: 4.4/8, #9; adults 18-49: 2.7, #T4). What does it mean?

Let's break it down piece by piece. In the example given for "My Name Is Earl," here's what each number signifies:

household rating = 4.4
household share = 8
household rank (for the night) = #9
adults 18-49 rating = 2.7
adults 18-49 rank (for the night) = tied for #4

2. So what does a 4.4 household rating mean?

A 4.4 household rating means that 4.4% of all households (that is to say homes with a TV set) watched this episode of "My Name Is Earl."

For the 2007-08 season, Nielsen Media Research has determined there are an estimated 112,800,000 television households in the U.S. This means that a single national household ratings point represents 1%, or 1,128,000 households.

With the above in mind, a 4.4 household rating equals 4.4% of 112,800,000 television households or 4,963,200 households.

3. So that's great and all. How do I find out exactly how many people (not just households) watched the show?

Unfortunately, we do not have access to the total viewers numbers on a daily basis.

Also keep in mind, the number of actual total viewers CANNOT be determined from the household rating or household share. Obviously since there is at least one person in a household, the total viewers will be "at least" 4,963,200 people in the above case.

3. So what does an 8 household share mean?

An 8 household share means that 8% of all households that happened to be watching TV watched this episode of "My Name Is Earl."

So in keeping with the above example, the 4,963,200 households that watched "My Name Is Earl" accounted for 8% of the television audience that was watching television at the time the show was on.

Also note that the share will always be larger than the rating. This is because the number of households watching television at any give time will always be less than those who own a television period.

4. So what does a 2.7 adults 18-49 rating mean?

A 2.7 adults 18-49 rating means that 2.7% of all adults 18-49 watched this episode of "My Name Is Earl."

For the 2007-08 season, Nielsen Media Research has determined there are an estimated 131,050,000 people between the ages of 18 and 49 in the U.S. This means that a single adults 18-49 ratings point represents 1%, or 1,310,500 people.

With the above in mind, a 2.7 adults 18-49 rating equals 2.7% of 131,050,000 adults between the ages of 18 and 49 or 3,538,350 people.

5. Okay, I've got all that. But how come the information I see here is different from the information I see elsewhere (i.e. Mediaweek, Zap2It.com, etc.)?

This is where a lot of confusion about ratings comes from. To better understand the answer, we must quickly go through what Nielsen Media Research does.

Nielsen collects data from two different samples: a "National Measurement" and a "Local Measurement." Households in each sample are given a device that tracks their viewing habits.

The 5,100 participating households in the "National Measurement" are outfitted with what's called a "Nielsen People Meter." This device measures two things - what program or channel is being watched and who in the household is watching. It accomplishes this by instructing each member in the household to press a button indicating that they have begun watching television on that particular set. This process allows Nielsen to electronically gather demographic information.

Every night this data is transmitted to Nielsen Media Research's Operations Center in Dunedin, Florida. Around 8:00 a.m. EST the next day Nielsen releases the preliminary "fast national" ratings from this data. This is the information you see reported every morning on The Futon Critic and Zap2It.

That afternoon, around 3:00 p.m. EST, Nielsen releases the "final national" ratings. These are the revised numbers which take into account various scheduling changes from across the country, most notably those due to live events (such as "Sunday Night Football" on NBC). Unfortunately, we do not have access to the "final national" ratings on a daily basis.

Nevertheless, the "final national" ratings are what you see reported in places like The New York Times, L.A. Times and USA Today as well as the various "weekly roundup" press releases we post to the site.

6. So far so good. Now what about that "Local Measurement" sample you mentioned?

The "Local Measurement" sample is used to track, as you might guess, information in a specific market, as opposed to the entire country in the "National Measurement."

Approximately 22,400-28,000 total households participate in the "Local Measurement" sample or about 400-500 households in each of 56 of the largest markets in the U.S. These are what are commonly referred to as the "metered markets" (click here for the complete list).

In total, the 56 metered markets account for 69.66% of all households in the U.S. This means that 30.34% of U.S. households are not included in the "Local Measurement" sample.

Homes recruited for the "Local Measurement" sample are NOT equipped with People Meters. Instead they're given more generic electronic meters, which can only measure what is being watched in the household NOT who in the household is watching what (i.e. demographic information). Because of this, only household ratings and shares can be reported.

In any case, every night this data is also transmitted to Nielsen and the following morning the "metered market" ratings are released. These numbers obviously will be different (but not obnoxiously different) from the "fast national" ratings also released by Nielsen. Generally speaking, since "metered market" ratings come from the largest urban areas, the numbers will skew in favor of more "urban" shows.

These are the household ratings and shares you see reported every morning at Mediaweek. But, as we mentioned previously, since demographic information (total viewers, adults 18-49, etc.) isn't obtained in the "Local Measurement" sample - Mediaweek also reports the "fast national" information for total viewers and adults 18-49 (even though they're from a different sample than the "metered market" ratings).

This hopefully clears up the differences between the numbers reported by The Futon Critic, Zap2It and Mediaweek.

7. One other thing - while I understand that The Futon Critic and Zap2It both report "fast national" ratings, how come sometimes the numbers are different by 1 or 2 digits?

The short answer is human error. Nielsen reports the "fast nationals" in half-hour form, meaning we have to average them to get the numbers for programs longer than a half-hour. Sometimes this leads to small variances.

8. So what about those paper diaries I hear about? Don't they count to?

Yes, but they're aren't a factor in the numbers that are electronically reported each day. Basically, paper diaries exist as a supplement to the "Local Measurement" sample.

Paper diaries are filled out during the months of November, February, May and July - periods generally referred to as "sweeps months." These diaries are used to record viewer habits, allowing each market to get some sort of demographic information.

As any regular TV viewer knows, the "sweep periods" are used by the networks to drum up ratings for their affiliate stations and often feature various stunts and special programming.

9. What about TiVos (or other DVR services)? Does Nielsen track those viewers?

As of January 1, 2006 Nielsen has added DVR viewership to its audience sample. In the case of "fast national" ratings, the data includes all DVR playback through 3:00 a.m. eastern time that day.

Overall, keep in mind that there are more than 112 million households in the U.S., only 20% of which own DVRs of some kind (read the story). The viewership of those households reflect the habits of those willing to buy a TiVo (or other DVR) and subscribe to its service, not a random sample of everyone in the U.S.

10. But if people are watching a show on their DVR, shouldn't it be counted no matter when it's replayed?

Yes and no. Remember that Nielsen's data is ultimately being used to determine the number of viewers being exposed to the advertising that airs on a particular program. DVRs allow viewers to "skip" those ads, for the most part nullifying any advertising viewership. Understandably then, for that reason, networks and advertisers will continue to make the "live" viewership the focus of their efforts.