Break out the Chardonnay: Footballers' Wives was ITV1's first big series of 2002

Different analyses produce different figures, but one carried out internally by the BBC suggested that average daily viewing per household fell 11 per cent in the first 13 days of this year compared to the first fortnight of 2001; BBC One's audience fell 12 per cent; ITV1's fell a whopping 26 per cent.

Other networks also suffered: on one analysis, viewing to Channel 4 amongst its key target audience of 16-34 year olds fell 38 per cent.

Ratings change

The problems stem from the biggest change in the measurement of TV ratings for 20 years, which was when Barb (the Broadcasters Audience Research Board) was set up and the BBC abandoned its own street surveys of viewing and joined ITV's existing electronic measurement system.

Under the modern system, a panel of thousands of homes agree to have a meter attached to every TV set in the house, recording what channels the set is tuned to and for how long; each member of the household has a button on a special remote control which they press whenever they enter or leave the room (there are also buttons for guests).

Channel 4 were left out in the cold about Shackleton's figures

Each night the central ratings computer rings up the meters and downloads the information on who has been watching what.

The current problems arose because for the first time ever the entire 5,100-strong panel has been changed. There have been difficulties recruiting enough homes to take part, with the result that the panel was under strength at the start of the year - only 3,800 homes.

Population make-up

What's more, the new panel reflects changes in the make-up of the population, like a five per cent fall in the number of 16-34 year olds, and has been changed in other ways, for instance by boosting the number of homes in London.

This all helps to account for the two-week suspension, while the new system was run in and its results checked for accuracy. But it doesn't necessarily explain the very big changes in viewing patterns.

Many in the broadcasting and advertising industries are sceptical: either the old ratings were wrong or the new ones are.

The BBC had to wait for news of EastEnders

There are several theories about what may have gone wrong. The new panel may not be very good yet at recording guest viewing, for instance, or noting the presence of every member of the family.

That could have an effect on BBC One and ITV1, whose schedules include more "appointment to view" programmes which the whole family and visitors sit down to watch together.

But the audience researchers themselves insist the new ratings, like the old, are accurate and that there's nothing wrong with their figures or their methods - and that leaping to conclusions on the basis of a single fortnight's figures is ridiculous anyway.

Channel 4 seems to be losing younger viewers of shows like Hollyoaks

We should, they say, give the new system time to settle down. And those big changes in viewing may reflect the reality: TV viewing is declining, as people find other things to do with their time (like watching DVDs or playing on their computers); the audiences for ITV1 and BBC 1 are going down as more people get digital television and spend time watching scores of other channels.

Torrid time

Does it matter? Yes. It matters to ITV, which has been having a pretty torrid time in the last 12 months - the last thing it needs is the widespread perception that its audience has fallen off a cliff.

It also matters to the advertisers, who buy billions of pounds' worth of airtime on the basis of the ratings: they will find it a lot more difficult to estimate how much to buy and at what price if the ratings are all over the place, and if doubts have been raised about their accuracy.

At the risk of advancing a rather metaphysical argument, it is of course possible that both old and new systems are accurate measures of "real" viewing - simply the real viewing of different members of the population.

More fun than TV?

But that isn't much help for practical purposes. For now, we all have three options. We can assume the ratings are wrong, and blame the researchers for fluffing the changeover to the new system. We can assume they're right, and conclude that we've all found better things to do with part of our time than watch the box.

Or we can suspend judgement in the hopes that in three months time some clearer pattern will emerge from the statistical fog.