In addition, advertising agencies sometimes organise their own research into whether viewers saw and remembered commercials for a particular advertiser. While it is not difficult to find out which programme people switch on, it's not nearly so easy to discover how closely they pay attention to television. In some homes TV is used as a clock - the set is on but no one is watching. In others, people may come and go while the TV is on catching perhaps only a few moments of a programme. Finding out whether people are actually watching is even more, difficult when it comes to the commercial breaks.
Some people slip out to put the kettle on or see to the baby as soon as the commercials start.
Even if the audience stay in their chairs for the commercial break, they may discuss the programme among themselves, pick up a paper or fit another piece into their jigsaw puzzles taking no notice of the advertisements. There is the added complication of video recorders, with time shifting. This helps to explain why, if you watch ITV for a whole evening, you will see the same advertisements several times. The advertisers hope that if they repeat their messages often enough they will reach everyone they are aiming at. Although, for many types of products and services, television is the leading medium, very few advertising campaigns are confined to TV alone.