A carefully selected sample of households (4,500) are provided with elecronics which monitors which channel they are watching. Each member of the household presses a button to indicate when they are actually in front of the box. The Broadcaster's Audience Research Board collates this data, weights it for socio-demographic reasons and publishes it overnight to all broadcasters and advertisers.

Surely in the 21st century with the vast majority of households using set top boxes, they could provide a more exact representation of who is watching what? X amount of 4,500 people (considering 50+ million in the UK watch TV) isn't enough to determine that 15 million watch 'this' and only 10 million watch 'that

I've never encountered anyone that has actually taken part in this kind of sample, so I am wary of where they actually do it.

They must do it across the country to make it representative, but I've never heard of anyone actually having the thing on the top of their TV.