Nielsen ratings are the audience measurement systems operated by Nielsen Media Research that seek to determine the audience size and composition of television programming in the United States using a rating system.

Nielsen Media Research was founded by Arthur C. Nielsen, a market analyst who started his career in the 1920s with brand advertising analysis and had expanded into radio market analysis during the 1930s, culminating in Nielsen ratings of radio programming, which was meant to provide statistics as to the markets of radio shows. The first Nielsen ratings for radio programs were released the first week of December 1947. They measured the top 20 programs in four areas: total audience, average audience, cumulative audience, and homes per dollar spent for time and talent.^[2]

In 1950, Nielsen moved to television, developing a ratings system using the methods he and his company had developed for radio. That method became the primary source of audience measurement information in the US television industry.

Nielsen television ratings are gathered in one of two ways:

Changing systems of viewing have impacted Nielsen's methods of market research. In 2005, Nielsen began measuring the usage of digital video recording devices such as TiVos. Initial results indicated that time-shifted viewing will have a significant impact on television ratings. A year later, the networks were not factoring these new results into their ad rates because of the resistance of advertisers.^[3]

Since about October 2017, Nielsen also began to track select programs from specific partners that air on subscription-based video on demand (SVOD) services such as Netflix. Partnering distributors insert a "tag" into the program to be distributed on these services which Nielsen can track without input from Netflix. Partnering distributors are able to determine if these ratings can be released publicly or not.^[4]

The most commonly cited Nielsen results are reported in two measurements: ratings points and share, usually reported as: "ratings points/share". There were 119.6 million TV homes in the U.S. for the 2017–18 TV season (Nielsen’s National Television Household Universe Estimates).^[5] The number of persons age 2 and older in U.S. TV households is estimated to be 304.5 million. A single national ratings point represents 1% of the total number. Nielsen re-estimates the number of television-equipped households each August for the upcoming television season.^[6]

Share is the percentage of television sets in use that are tuned to the program of Households Using Television (HUT) or Persons Using Television (PUT) who are tuned to a specific program, station or network in a specific area at a specific time.^[7][8] For example, Nielsen may report a show as receiving a 4.4/8 during its broadcast; this would mean that 4.4% of all television-equipped households (that is to say homes with a TV set, not total number of people), regardless of the TV being on or not, were tuned in to that program, while 8% of households that were watching TV at that time were watching the specific program.^[9]

Because ratings are based on samples, it is possible for shows to get a 0.0 rating, despite having an audience; the CNBC talk show McEnroe was one notable example.^[10] Another example is The CW show, CW Now, which received two 0.0 ratings in the same season. In 2014, Nielsen reported that American viewership of live television (totaling on average four hours and 32 minutes per day) had dropped 12 minutes per day compared to the year before. Nielsen reported several reasons for the shift away from live television: increased viewership of time-shifted television (mainly through DVRs) and viewership of internet video (clips from video sharing websites and streams of full-length television shows).^[11]

Nielsen Media Research also provides statistics on specific demographics as advertising rates are influenced by such factors as age, gender, race, economic class, and area. Younger viewers are considered more attractive for many products, whereas in some cases older and wealthier audiences are desired, or female audiences are desired over males.

In general, the number of viewers within the 18–49 age range is more important than the total number of viewers.^[12][13] According to Advertising Age, during the 2007–08 season, ABC was able to charge $419,000 per commercial sold during its medical drama Grey's Anatomy, compared to only $248,000 for a commercial during CBS' CSI: Crime Scene Investigation, despite CSI having almost five million more viewers on average.^[14] Because of its strength in young "demos" (demographic groups), NBC was able to charge almost three times as much for a commercial during Friends as CBS charged for Murder, She Wrote, even though the two series had a similar amount of total viewership during the two seasons they were on the air concurrently.^[12] Glee (on Fox) and The Office (on NBC) drew fewer total viewers than NCIS (on CBS) during the 2009–10 season, but earned an average of $272,694 and $213,617 respectively, compared to $150,708 for NCIS.^[15]

Nielsen also provides viewership data calculated as the average viewership for only the commercial time within the program. These "Commercial Ratings" first became available on May 31, 2007. Additionally, Nielsen provides different "streams" of this data in order to take into consideration delayed viewing (DVR) data, at any interval up to seven days.^[16] C3 was the metric launched in 2007, and refers to the ratings for average commercial minutes in live programming plus total playback by digital video recorder out to three days after.^[17] By the end of 2012, some television executives wanted to see C7, ratings for live plus seven days, with CBS Corporation chief executive officer Les Moonves making the claim C7 made ratings increase by 30%.^[18]

The American television measurement by Nielsen is based on three different methodological approaches. In the 25 TV markets with the highest sales (e. g. New York, Los Angeles, Chicago, Denver) the Local People Meter (LPM) is measured. Individuals register individually, the measurement is carried out on 365 days over 24 hours.^[19] The SET Meter (Diary & Electronic) is used in 31 smaller markets (such as Nashville, Salt Lake City). In four sweeps in the months of February, May, July and November, target group data are collected with the diary and validated with the data of the devices (TV set on/off) in the participating households.^[19] In the 154 TV markets with the lowest sales (e. g. Harrisburg, PA or Honolulu) the use of TV is only recorded by means of a diary survey.

Each year, Nielsen processes approximately two million paper diaries from households across the country,^[20] for the months of November, February, May and July—also known as the "sweeps" rating periods.^[21] The term "sweeps" dates from 1954, when Nielsen collected diaries from households in the Eastern United States first; from there they would "sweep" west.^[22][23] Seven-day diaries (or eight-day diaries in homes with DVRs) are mailed to homes to keep a tally of what is watched on each television set and by whom. Over the course of a sweeps period, diaries are mailed to a new panel of homes each week. At the end of the month, all of the viewing data from the individual weeks is aggregated.

This local viewing information provides a basis for program scheduling and advertising decisions for local television stations, cable systems, and advertisers. Typically, the November, February and May sweeps are considered more important; nevertheless, the July sweeps can have local impact in regard to personnel.^[21]

In some of the mid-size markets, diaries provide viewer information for up to two additional "sweeps" months (October and January).

There is some public critique regarding accuracy and potential bias within Nielsen's rating system, including some concerns that the Nielsen ratings system is rapidly becoming outdated because of new technology like smartphones, DVRs, tablet computers and Internet streaming services as preferred or alternative methods for television viewing. In June 2006, however, Nielsen announced a plan to revamp its entire methodology to include all types of media viewing in its sample.^[25]

Since viewers are aware of being part of the Nielsen sample, it can lead to response bias in recording and viewing habits. Audience counts gathered by the self-reporting diary methodology are sometimes higher than those gathered by the electronic meters which eliminate any response bias.

Another criticism of the measuring system itself is that it fails the most important criterion of a sample: it is not random. A small fraction of the population is selected and only those that accept are used as the sample size. In many local areas during the 1990s, the difference between a rating that kept a show on the air and one that would cancel it was so small as to be statistically insignificant, and yet the show with the higher rating would survive.^[26] In addition, the Nielsen ratings encouraged a strong push for demographic measurements. This caused problems with households that had multiple television sets or households where viewers would enter the simpler codes (usually their child's) raising serious questions to the quality of the demographic data.^[26] The situation further deteriorated as the popularity of cable television increased the number of viewable networks to the extent that the margin of error has increased, because the sampling sizes are too small.^[26][27][28] Compounding matters is that of the sample data that is collected, advertisers will not pay for time shifted programs (those that are recorded for replay at a different time),^[29] rendering the "raw" numbers useless from a statistical point of view. Even in 2013, it was noted that Internet streams of television programs were still not counted because they had either no ads (such as Netflix) or totally different advertising (such as Hulu) than their television counterparts, effectively skewing the raw data on a show’s popularity.^[30]

A related criticism of the Nielsen ratings system is its lack of a system for measuring television audiences outside homes, such as college dormitories, transport terminals, bars, prisons and other public places where television is frequently viewed, often by large numbers of people in a common setting. In 2005, Nielsen announced plans to incorporate viewing by away-from-home college students into its sample. Internet television viewing is another rapidly growing market for which Nielsen ratings fail to account for viewers. iTunes, Hulu, YouTube, and some of the networks' own websites (such as ABC.com and CBS.com) provide full-length web-based programming, either subscription-based or ad-supported. Though web sites can already track popularity of a site and the referring page, they cannot track viewer demographics. To both track this and expand their market research offerings, Nielsen purchased NetRatings in 2007.^[31] However, as noted in a February 2012 New York Times article, the computer and mobile streams of a program are counted separately from the standard television broadcasts, further degrading the overall quality of the sampling data. As a result, there was no way for NBC to tell if there was any overlap between the roughly 111.3 million traditional television viewers ^[32][33] and 2.1 million live stream viewers of Super Bowl XLVII.^[34]

Responding to the criticism regarding accusations by several media executives (including Viacom CEO Phillippe Dauman and former Fox Entertainment Group chief operating officer Chase Carey) that it failed to count viewers watching television programs on digital platforms, Nielsen executive vice president of global product leadership Megan Clarken stated in an April 2015 summit by the Coalition for Innovative Media Measurement that the company is able to count digital viewers in audience and demographic reports, but unable to do so under the current set of rules devised by networks and advertising industries last revised in 2006. As such, Nielsen can only count viewership for television-originated broadcasts, and must exclude viewers who watch programs on digital platforms if the program does not have an identical advertising load or a linear watermark.^[35]

After Nielsen took over the contract for producing data on Irish advertising in 2009, agencies said that they were "disastrous" and claimed that the information produced by them is too inaccurate to be trusted by them or their clients.^[36]

In 2004, News Corporation retained the services of public relations firm Glover Park to launch a campaign aimed at delaying Nielsen's plan to replace its aging household electronic data collection methodology in larger local markets with its newer electronic People Meter system. The advocates in the public relations campaign claimed that data derived from the newer People Meter system represented a bias toward underreporting minority viewing, which could lead to a de facto discrimination in employment against minority actors and writers. However, Nielsen countered the campaign by revealing its sample composition counts. According to Nielsen Media Research's sample composition counts, as of November 2004, nationwide, African American households using People Meters represented 6.7% of the Nielsen sample, compared to 6.0% in the general population. Latino households represent 5.7% of the Nielsen sample, compared to 5.0% in the general population. By October 2006, News Corporation and Nielsen settled, with Nielsen agreeing to spend an additional $50 million to ensure that minority viewing was not being underreported by the new electronic people meter system.^[37]

In 2011, CBS and Nielsen proposed a model consisting of six viewer segments which according to their empirical research are more relevant for advertisers than older models based on gender and age. The segments are based on user behavior, motivations, and psychographics. It is argued that the model can increase reaching the desired audience as well as message recall and advertisement likeability.^[38]

The table below lists television shows in the U.S. with the highest average household Nielsen rating for each television season.^{[39][40][41][42][43]}

(total viewership, exclusive of demographics)