question: How do radio stations, over-the-air TV channels, etc. measure their viewership of passive subscribers?
comment: There are companies that pay people to keep devices on them that detect what they're watching. If you get enough people using them, you can extrapolate to get a decent estimate of how many people are watching what.
passages: In 2005, the FCC completed a federal study on the media markets in the United States. Using the data, the FCC created a list of counties in each state where out-of-market television stations are significantly viewed by residents who are using antennas. Whether or not they are cable or satellite subscribers was not deemed important in their study. The study also looked at the history of viewership of the original Community Access Television (CATV) installations throughout the country, the predecessor of Cable television. Today's cable television content is more focused on premium channel television programming than the original purpose of picking up local programming from television stations in a specific area.
   Nielsen Media Research. It is used by media planners and buyers, advertisers to appropriate the ratings of channels when individual viewership is calculated. This term is usually used in the US to represent average percentage of People using TV across all channels within predefined time period.
   A similar term used by Nielsen Media Research is the Designated Market Area (DMA), and they control the trademark on it. DMAs are used by Nielsen Media Research to identify TV stations that best reach an area and attract the most viewers. There are 210 Nielsen DMAs in the United States, 70 of which are metered (in other words, viewership in these markets are estimated automatically instead of through the archaic diary system still in use in the smaller markets).
   The Nielsen TV Ratings have been produced in the USA since the 1950-51 television season and statistically measure which programs are watched by different segments of the population. The most well-known portion is the "diary". During the four "sweeps" months of February, May, July and November, Nielsen interviewers in Oldsmar, Florida and Radcliff, Kentucky ask homes to participate in filling out a diary of the programs watched in their home for a one-week period.
   Although much of the audience research data is normally only available to subscribers and prospective advertisers, basic information is published for the general public, often as topline survey findings. The type and depth of freely available information varies across geographic markets. Audience research for broadcast media is provided to prospective advertisers via the networks or via a media buying group. A limited amount of basic audience data is available to the general public through statutory authorities or media organisations.
  
  BULLET::::- Notes: Also see Nielsen Media, for "Trends in Canadian TV Viewing"
  
  Section::::Advertising media scheduling.
   Four basic methods of data collection are used to survey broadcast audiences, namely interviews, diaries, meters or scanning and modelling. Research companies employ different methodologies depending on where and when media is used and the cost of data collection. All these methods involve sampling – that is taking a representative sample of the population and recording their media usage which is then extrapolated to the general population.
   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.
   Nielsen's formula for PUT is the number of persons viewing TV divided by the total persons universe i.e. the television rating divided by the total share of television in a particular demographic area.
   The project included a sample of 1000 men and women aged 18–54 drawn from respondents who completed GfK MRI's widely used "Survey of the American Consumer," and employed eDiaries in which participants recorded their media behavior at 30 minute intervals over 10 days. That data was fused with existing media measurement services. This "hub and fusion" approach to cross-platform media measurement provides a time-based way of understanding consumers' media behavior. The study ran from September 2010 to February 2011.
  
  On August 16, 2011, GfK MRI and Nielsen announced they made equity investments in MBI, supporting USA TouchPoints.
   Section::::New media.
  
  Nielsen//NetRatings measures Internet and digital media audiences through a telephone and Internet survey. Nielsen BuzzMetrics measures consumer-generated media. Other companies collecting information on internet usage include comScore, Wakoopa, and Hitwise, who measure hits on internet pages. Companies like Visible Measures focus on measuring specific types of media; in the case of Visible Measures, they measure online video consumption and distribution across all video advertising and content. GfK offers Cross Media Measurement Solutions that allows to attribute offline sales to media exposure across TV, Internet and Mobile utilizing its proprietary LEOtrace technology.
   Section::::Ratings.:Online viewership.
   In 2005, ACNielsen initiated their MVP (Media Voice Panel) program. Panel members carry an electronic monitor that detects the digital station and program identification codes hidden within the TV and radio broadcasts they are exposed to. At night, members place the monitor in a cradle that sends the collected data through the home's electrical wiring to a relay device that transmits it by phone, making it one of the first practical uses of electrical wiring as a home network. With an approximately one week notice to members, the MVP program ended on March 17, 2008.
   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). 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.
   Research companies employ different methodologies depending on where and when media is used and the cost of data collection. All these methods involve sampling – that is taking a representative sample of the population and recording their media usage which is then extrapolated to the general population. Media owners typically share research findings with prospective advertisers, while selected findings are available to the general public via the media research company or an entity, such as a broadcast commission, established to administer the audience research process.
   The Nielsen sample included roughly 1,700 audiometer homes and rotating board of nearly 850 diary respondents, by the early 1980s. Nielsen launched its Nielsen Homevideo Index (NHI) in 1980 to measure cable, pay cable, and VCRs, and the NHI began offering daily cable ratings in 1982. Nielsen's continued to advance with steady changes into the mid 2000s (decade). Along with changing their counting methods, Nielsen also started emphasizing their sample in 2003 in reaction to census shifts and requests from some industry sectors. Nielsen's automated Local People Meter (LPM) technology was introduced in New York and Los Angeles. The LPM improved the method of measurement from active and diary-based to passive and meter-monitored. More importantly, the LPM provides accurate measurements to particular local markets, verse a nationwide sample from the People meter. While diary-based surveys concentrated on quarterly sweeps periods, the industry has been pushed toward year-round measurement, due to the automated LPM system.
   BULLET::::- In Malaysia, no single, official currency for measuring TV audiences and two competing companies provide data, using different methodologies, namely GfK Malaysia and Kantar Media; radio surveys are carried out by GfK Malaysia.
  
  BULLET::::- In the Netherlands Press, TV and radio measurements are handled by GfK.
  
  BULLET::::- In New Zealand GfK measures radio audiences, while ACB McNair measures TV audiences.
   There is no definitive list of every radio and television station in the world. The National Association of Broadcasters cites the estimate from the U.S. C.I.A. World Fact Book, which reports that "as of January 2000, there are over 21,500 television stations and over 44,000 radio stations." (CIA World Fact Book references – Radio, TV)
  
  In the United States the FCC provides a list of "Licensed Broadcast Station Totals (Index) 1990 to Present," which may be found here. According to the FCC report –
   BULLET::::- In Turkey, TV measurement is done by TNS (Kantar Media), radio by Nielsen.
  
  BULLET::::- In the UK, television measurement is administered by the Broadcasters' Audience Research Board via a metered panel and radio by RAJAR, using a diary system. The NRS (National Readership Survey) measures newspaper and magazine readership.
  
  BULLET::::- In the United States, TV and radio measurement is carried out Nielsen Media Research (the radio component was formerly carried out by Arbitron), and digital signage by TruMedia and CognoVision. Stratacache uses audience measurement technology to build reports for digital signage.
   TV + OOH: BARC India now measures and reports TV viewership that happens in social hot-spots like restaurants, pubs, and bars across 120+ Urban towns and cities.
  
  Spot Trek: Provides reports on advertising monitored spots to the agency 
  
  Section::::BARC: TV Audience Measurement Methodology.
  
  The entire BARC India process can be broadly bucketed as follows:
   PUTs is calculated by considering the average audience figures gauged from the peopleometer, for all channels during a particular time period and adding them together to get the cumulative number. Put is used to calculate the demographic persons rating. Almost all media scales are technically based on person's ratings. It is observed that the percentage rating remains constant from year to year. If changes are observed, then they are slight in nature and only due to changes in viewing habits.
  
  Section::::PUT and PVT.
   BULLET::::- "Audience share:" The number of listeners (or viewers) for a given channel over a given time period, expressed as a percentage of the total audience potential for the total market. (The audience share is normally calculated by dividing a given channel's average audience by the average audience of all channels).
   BULLET::::- In Germany TV audience measurement is done by Gesellschaft für Konsumforschung (known as GfK).
   Nielsen ratings (carried out since 1947) provide another example of public surveys in the United States. Nielsen ratings track media-viewing habits (radio, television, internet, print) the results of which are used to make decisions by and about the mass media. Some Nielsen ratings localize the data points to give marketing firms more specific information with which to target customers. Demographic data is also used to understand what influences work best to market consumer products, political campaigns, etc.
  
  Following the invention of the telephone survey (used at least as early as the 1940s),
   Section::::aMap chosen as audience measurement currency by Eurodata TV worldwide.
  
  Eurodata TV Worldwide has released, ‘One Television Year in the World’ a handbook on TV audience measurement data across the world. 
  
  “Eurodata TV Worldwide” is the international data bank of TV programmes and audiences, which now covers over 2000 channels throughout 80 territories and provides daily program information including: content, production, international distribution and the audience levels for targeted programs, all data emanating directly from the authorized institute based in each country. For India the institute is aMap. 
  
  Section::::Connectivity data.
   BULLET::::- "Cumulative audience (CUME):" The number of "different" listeners (or viewers) in a given time period; also known as "reach".
  
  BULLET::::- "People Using Television (PUT)": The number of people (or households) tuned to any channel during a given time period.
  
  Out-of-home media
  
  BULLET::::- "Opportunities to see (OTS)" - a crude measure of the number of people who were exposed to the medium, For example, the number of cars that drive past an outdoor billboard in a given time period
  
  Internet and digital media 
  