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RAJAR: Made to measure
A basic overview of how audience figures are worked out in the UK and some of the terminology used.
Rajar stands for the Radio Joint Audience Survey. It is funded partly by the BBC, the Commerical Radio Companies Association and the Radio Advertising Bureau and is the industry standard measure of audience numbers.
Rajar measure the number of people who listen to a radio station and how long they listen for. Each station has a TSA, which stands for a Total Survey Area. That is a defined geographical area that they cover, either defined by the station or by the licence issued by Ofcom.
Rajar conducts its research by sampling people within a TSA. They are given a diary and asked to fill in when they listened to the radio and what station they listened to. The results of each person's diary are then taken and weighted to match the demographic of the area being sampled. So if there are more 24 year olds in an area than 34 year olds, the 24-year-old's diary will carry a greater weighting.
Rajar results are split into three distinct sets of figures. The Reach is the number of adults (aged 15+) who listen to more than five minutes of the radio station within a week However that five minutes must be within a fifteen minute period. So it can't be someone who tunes in for just one minute Monday to Friday.
Reach is often given as a percentage of the total number of adults within the TSA.
The second set of figures are Share. This measures the success of the station against others in the area - in other words it is a good way to compare stations. Share is calculated by taking the total number of people listening to the radio and then working out the percentage of those listening to a particular station.
You'll often see BBC v Commercial radio Share information in the papers - it is so close to the 50% mark that every time the Rajar results are published people watch to see who is winning and who is losing.
The third set of figures are the Total Weekly Hours. This is simply a case of adding up the number of listeners and how long they listen for. If you divide this by the Reach - you get an average listening hours; ie the average length someone will listen to the station.
These figures are used by station management to deem the success of individual presenters. They also help advertising agencies decide which stations to buy airtime on - so in commercial radio they are particularly important. You'll find higher sampling rates for commercial stations TSAs.
Results are published every three months, but the length of the survey period depends on the size of the station. National stations will have a complete set of new figures every three months - smaller stations have their figures worked out across a six or twelve month period.
General station information is made available on the Rajar website - and is also published in trade magazines. More specific information is available only to Rajar subscribers; and certain bits of data are restricted just to the station concerned.