In the UK, audience measurement for all television viewing (ITV, BBC, Channel 4, channel 5, GMTV, cable and Satellite) is monitored by the Broadcaster's Audience Research Board (BARB). BARB is a non-profit making body set up as a joint venture between ITV and BBC and includes representatives from agencies and advertisers to ensure that the data collected is compiled and presented free from bias.
Audience measurement is based on the viewing habits of a selected number of households; 4,485 in all across the whole country. These households are selected on the basis that they are representatives of the UK population in terms of age, gender, number of children and income.
Normal viewing habits are measured using a "people meter," an electronic device which can detect which channel is being watched , for how long and by whom in the household. The meter also records when the household is on holiday, any programmes that are videoed and watched later, and even the visitors to the house.
The information about the programmes watched is transmitted nightly via a telephone line to a research center where it is scaled up to give an accurate picture of what the 55 million people in the UK are watching. The figures are made available to advertisers and programme makers by 10am the following day.