As one of the 4,500 households which is part of the monitoring system, I hope I can clear a couple of things up.
The system works via a set-top box. Basically, when a person comes into the room you press a pre-programmed button to add them to one of eight slots (which automatically tell the system the age and sex of the viewer) or, for guests, you program it manually.
Each TV in the house has a box, which also takes a feed from any VCRs and Digiboxes, etc. They then register each channel change or when a person enters or leaves the room (as long as they remember to press the appropriate button).
When the TV is turned off, a radio signal is sent to one main box in the house, which is connected to the phone line.
At around 2am each day, all the information about that day's viewing habits is sent to a company called RSMB who collate the data for BARB. It does this by dialling a freephone number.
Generally, the data is reasonably accurate - I think they try to get as broad a range of viewers as possible, but obviously, without monitoring everyone's viewing habits, it's impossible to get perfect data. As Lee pointed out, he and his mates might watch MTV2 loads - but then again there could be whole groups elsewhere in the country who don't even know the channel exists.
Of course, there are problems with Sky Digital monitoring. Of the 23 million? households in the UK, only 4,500 have monitoring equipment. If I remember correctly, about 5 million households now have Sky Digital, which would therefore mean that there are only about 900 households which it takes its figures from. And obviously, given the sheer number of channels available, it's very difficult to get accurate viewing figures.
Hope this helps - anyone who want's more info can e-mail me on
dbfriends@hotmail.com
And celestial posted while I was typing this reply... I don't really know how the ad break bit works, but I suspect the figures are generally wrong. If you tell the machine that no-one is watching, it flashes "Who Is Present?" until you press a button on again - do it too often and RSMB call you up. So we generally leave ourselves "on the box" while going to get food or whatever. This would therefore mean the ad break figures are a bit inaccurate.
And there was another post while I typed the extra bit... you are told to register that you are in the room, not watching the TV. Pressing the button keeps you on for as long as you stay, but the box flashes up "Check Viewers" and "Any Guests?" every ten minutes just to remind you.
