Mark and Lard: Recent Rajar winners for Radio 1

Audiences are measured for more than 260 radio stations, but since no two of them seem to have the same transmission areas information from the diaries has to be analysed for more than 600 separate listening areas.

Shortcomings

Not surprisingly perhaps, Rajar is also the most expensive audience survey in the world (at �4 million a year) compared to the size of the industry it serves. Even so it has its shortcomings.

Though it publishes data every quarter, the smallest stations only get audience figures once a year - and then based on sample sizes of only 300.

The system still can't produce proper listening figures for a particular programme on a particular day - only an average of the audience for the time slot over three months. And there's no way of telling whether someone listened to a particular station on FM, on digital or over the internet.

What's more the diary could soon be superseded by something even more accurate, an electronic meter.

Chris Tarrant's ratings on London's Capital FM come up for scrutiny...

Unlike the "people meters" used to measure television viewing, however, these are not attached to a particular set but to the individual, worn like a wristwatch or a pager, because for most people radio listening happens in many different places and on many different radios during a day.

Swiss meters

The first country to measure with meters is Switzerland, where they started in January.

The wristwatch-style device records what its wearer hears, then sends the data back to a central computer overnight. the computer also records samples of all the local stations' transmissions to compare with the information sent back by the meter and work out which stations it overheard.

A rival US system works by recording a special inaudible code transmitted alongside stations' programmes.

One advantage is that the meter can distinguish between the same programme transmitted on different frequencies (FM, say, and digital), which is important for the operators of the fledgling digital multiplexes.

...as do those of flagship Radio 4 shows such as PM

But meters have their problems. How accurate will they be in practice? Can they distinguish between a radio programme and piped music in a shopping mall? Will people be happy to wear them? Will they remember to keep them charged?

And, above all, how much will they cost? Jane O'Hara, who runs Rajar, says introducing meters could increase the cost of the survey by as much as three times.

Trade-off

The radio industry clearly couldn't afford that, so in the end there will have to be a trade-off, and it may be the smaller stations which will suffer.

Perhaps some stations' audiences could be measured by meters, others by diaries.

Perhaps there could be several different surveys, each using a different methodology, under the Rajar umbrella.

Perhaps costs could be saved by reducing the numbers of people surveyed or by cutting those 600-plus areas to something more manageable - even if in larger survey areas small stations' audiences would inevitably show up as smaller percentages of the total population.

The industry is now planning trials of the meters. No major changes are likely for a while yet: the current contract to carry out the survey - with the research company Ispsos/RSL - runs out next year, but can be extended for a further two years.

But the one thing the radio industry will be desperate to avoid is anything which knocks confidence in the accuracy of its research, especially among advertising agencies.

A solid audience "currency" is vital for commercial radio.

Whatever else happens, a reformed Rajar must produce audience figures advertisers will believe in.