TV rating is the percentage of total audience (or households) with their TV sets tuned to a particular station/channel or program for a specified length of time over the total audience (or households) that have TV. As an important indicator of the attention economy, TV ratings are the currency of buying and selling of commercial airtime, provide an indication of TV program quality, and play a significant role in TV programs ‘revisions, improvements and scheduling decisions. TV rating is expressed as a simple percentage calculation, but it involves using comprehensive scientific methods in a series of processes that includes Establishment Survey, sampling, panel creation, data collection, data processing, etc.
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Establishment Survey Establishment Survey, aimed at understanding TV viewership universe and other detailed information of TV markets, is an essential part of the measurement service. Generally, an Establishment Survey is conducted by CSM Media Research at the initial stage of setting up a TV audience measurement system. After that is conducted on a regular annual basis (every two years for some diary panels in small cities) to monitor changes in TV market over time and for projection of the measurement system's universe estimates.The Establishment Survey is the foundation of the TAM service, and has the three major objectives: 1) to provide universe estimates for the TV panel, including television ownership, TV channel reception capability, ownership of television related equipment, and detailed demographic information;. 2) to obtain targets for the results of the survey for various marginal and interlaced demographic and television reception characteristics to which the TAM panel should conform; and 3) to provide a sample of households of known characteristics, to be used for TAM panel recruitment and maintenance.
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Sampling and Panel Creation To give a reliable measurement service, a Panel must be representative of the population from which it is selected, apart from any deliberate disproportionate sampling. The achievement of a representative Panel is a two - stage process. First by employing a high quality probability sample design and then by ensuring that the panel is, and remains, consistent with population values for a number of characteristics. Generally, CSM uses a stratified multi-stage PPS random sampling method to get the household samples and set up a panel. A panel data follows a given sample of individuals over time, and thus provides data in different time periods on each individual in the sample. Panel data possesses advantages over cross-sectional or time-series data by reducing considerably the omitted variable bias caused by sampling procedures, and offers statistical advantages. TV audience measurement often employs panel survey, and the sample is relatively stable over time except a periodic turnover of a propotion of the panel. Continuous viewing data will be collected from panel homes on the basis of 24 hours a day, 365 days a year.
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Data Collection Diary Method The diary method uses diary cards to gather information on TV viewing, and it requires all household members ages 4 or above in panel homes to record the TV channels they watched and the watching time throughout a normal day. TV viewers can write down the code of TV channels they watched, and mark the corresponding viewing time band on CSM’s diary card. Each diary card can record one week’s (seven days) viewing data for an individual. A time unit of 15 minutes is set for diaries, and if an individual watches one channel for more than 8 cumulative minutes during any particular 15 minute period, this channel will be credited with 15 minutes of viewing. Interviewers will collect the completed diary cards on a regular weekly basis. People Meter Method The people meter method uses people meter device to gather information on TV viewing for all household members ages 4 or above in panel homes. The people meter device automatically records all uses of every television set in the panel on a second-by-second basis. The detection of TV set on/off and channel switching is completely automatic, while each viewer is required to press a remote control handset to indicate presence. Viewing data stored in the device will be transferred to CSM server by overnight polling via telephone line or GPRS, and the clients will get the viewing data on the morning of the next day. CSM currently uses three types of measuring techniques: DFM, SI-Code, and Audio Matching.DFM (Direct Frequency Measurement): DFM is used for measuring analog television signals, and it identifies TV channels by means of metering their frequencies and comparing these against the channel map for the TV set or other input source being monitored.SI-code (Service information code): SI-code technique is used for measuring digital television signals. The people meter detects the SI-code sent from the settop box, and uniquely identifies the channel being watched. The people meter receives information directly from the settop box without additional procedures. This technique is very effective and highly accurate.Audio Matching: Audio Matching technique is used for measuring both analog and digital television signals. It identifies the viewing channel by matching the audio from the TV set with a “library” or “reference set” of audio signals collected from the devices connected to the TV set. The people meter collects the audio in the form of “samples” and this information is passed back to the processing system by overnight polling. Reference sites will be set up to record each monitored channel and the matching between the reference data and audio samples collected from the panel homes identifies the channel being watched.
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Data Processing Data processing is an important part of the TAM service, and includes the following three major procedures:： (1) Data entry and cleaning: raw data from the TV audience survey will be entered into the computer system (only for the diary method, and the people meter method can transfer the raw data to the computer system automatically). To ensure data quality, the data cleaning process will be conducted after the data entry process is completed to rule out data entry errors or logical errors. (2) Data integration: After the data cleaning phase, comes the integration process. Viewing data, demographic information, and TV program information will be integrated into a comprehensive TV Audience Database. (3) Weighting and calculation: the weighting procedure will be applied to the survey data to restore it to agreed population projections. The weighting variables often include age, sex, etc. After the weighting, a variety of calculations will be performed on the raw data from the TV audience survey to produce different rating data.
