frequently asked questions about nielsen ratings
(last updated: sunday, september 19, 2010)

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: "The Office" (7.30 million viewers, #8; adults 18-49: 3.7, #T3). What does it mean?

Let's break it down piece by piece. In the example given for "The Office," here's what each number signifies:

total viewers (in millions) = 7.30
viewership rank (for the night) = #8
adults 18-49 rating = 3.7
adults 18-49 rank (for the night) = tied for #3

The aforementioned data is mostly straightforward: 7.30 million people watched that night's episode of "The Office" live or on their DVRs before 3:00 AM ET (more on this in a second). Among viewers ages 18-49, it drew a 3.7 rating, meaning 3.7% of viewers in that age group watched said episode live or on their DVRs before 3:00 AM ET (also more on this in a second).

2. Sometimes I see viewership denoted as something like 4.4/8. What does that mean?

More than likely, you're looking at a show's household rating and share, not its actual viewership. Ratings and share are percentages not flat numbers. A 4.4 household rating/8 share means that 4.4% of all households (that is to say homes with a TV set, not total number of people) watched the indicated program, while among those households watching TV at the time 8% of them watched.

Note the distinction here: a rating is based the entire sample (whether they're watching TV or not) while a share is based on those actively watching television.

To break it down even further, for the 2010-11 season, Nielsen Media Research has determined there are 115.9 million television households in the U.S. So a 4.4 household rating means that 4% of those 115.9 million homes watched the program, or 4.636 million households (0.04 X 115.9 = 4.636). Furthemore, those 4.636 households also represent 8% of the people actively watching television at the time.

And if you break out your freshman algebra (4.636/57.95 = 8/100), you can also determine that about 57.95 million households were watching TV at that time with the rest of the 115.9 million households (115.9 - 57.95 = 57.95, hey that turns out to be half!) weren't watching TV at all.

3. So what does a 3.7 adults 18-49 rating mean?

If you read question #2, you'll remember that ratings are percentages not flat numbers. So a 3.7 adults 18-49 rating means 3.7% of viewers ages 18-49 watched the broadcast. For the 2010-11 season, Nielsen Media Research has determined there are 131 million adults 18-49 in the U.S. so 3.7% of them would be 4.847 million (.037 X 131 = 4.847). Or to put it another way, each adults 18-49 ratings point equals 1.31 million viewers.

4. What's the difference between metered-market ratings and fast national ratings?

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 9,000 participating households (over 18,000 people) 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 AM ET the next day Nielsen releases the preliminary "fast national" ratings from this data. This is the information you see reported every morning on the site.

That afternoon, around 3:00 PM ET, 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). These "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.

5. 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.

While metered market ratings are less prevalent in terms of primetime ratings nowadays, they are used in our late-night ratings reports each day.

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

Yes, but they're not 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 (i.e., what it doesn't get from its electronic meters).

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.

Markets outside the 56 metered areas also use them regularly as they cannot afford Nielsen's electronic service.

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

The "fast national" ratings were report each day includes DVR viewership through 3:00 AM ET that night. Furthermore, advertising is sold on what's known as a "C3" basis. This means that all commercial viewership in the first three days of a broadcast (live or DVR) is used. So yes, DVR viewership is most definitely factored in.

Nevertheless, it's important to keep in mind that DVRs are only in 38% of TV households, meaning the overwhelming majority of people doesn't have or use them. And the numbers reflect this: a recent report indicates DVR viewership on the broadcast networks only accounts for about 11.6% of a show's ultimate audience.

8. But that doesn't explain why shows I don't care about do better than shows I do.

There's two big things fans need to remember when it comes to ratings. First and foremost, ratings are NOT an indication of a show's overall reach, the devotion of its fanbase or any other anecdotal measurement. Ratings are designed to see how many people are watching the commercials on a TV show, you know, the things that pay for the TV shows in the first place. With that in mind, people who skip ads on their DVRs, watch shows online, download them illegally, view them on DVD, etc. aren't as relevant when it comes to advertising money.

In 2008, the broadcast and cable networks made a collective $67.92 billion of traditional advertising. The rest - online advertising ($1.63 billion), DVD ($450 million), iTunes ($180 million) - is just peanuts by comparison. Until that paradigm changes, ratings are the most critical factor for a show's survival.

Secondly, if you are reading this, you probably are not the average TV viewer. We get the e-mails all the time: "everybody I know watches show X, there's thousands of web sites devoted to X and X is always a bestseller on iTunes and/or Amazon, so Nielsen must not be counting viewership correctly." Or the converse: "I don't know anybody that watches show Y, there's very few web sites devoted to Y and Y is never a bestseller on iTunes and/or Amazon, so Nielsen must not be counting viewership correctly."

There's a big problem with these types of assumptions. First and foremost, the overwhelming majority of TV viewers do not own a DVR, do not watch shows online and do not purchase TV shows on DVD and/or download TV shows. I'm guessing if you are reading this, at least one of those habits applies to you and the aforementioned "everybody you know." Furthermore, a quick glance at the 2000 Census data will tell you that only about 1% of America is "like you" in that they have the same age, race, relationship and housing occupancy.