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.
-
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.
-
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.
-
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.
-
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.
