Measures of radio audiences

The data from diaries is converted into several types of audience measure, each of which is useful for a different purpose. The main measures are:

 

  • average audience
  • reach, or cumulative audience
  • share
  • duration
  • impressions
  • frequency – average and distribution
  • loyalty

 

Average audience

The average audience is simply the average number of people listening to a particular station in a particular time period. This is usually expressed as estimated thousands of listeners, but sometimes as a percentage of the relevant population. (For television, it’s the other way round.) The time period can be

  • a quarter-hour,
  • a time zone – which can be defined in any way, but often corresponds to one program segment, of several hours,
  • a whole day – sometimes excluding any hours when the station is not on air,
  • a week.

These average audience figures can be calculated for any demographic group. In the above example, with three age groups for each sex, there would be average audience figures for each of these 6 groups separately, plus figures for each age group (both sexes combined) and each sex (all age groups combined), as well as a total figure. There would be figures for each main station, with less popular stations combined as “other”. For each station and each demographic group, there would be estimates for each quarter-hour of the week, every time zone, each day, and a weekly average. That’s a lot of numbers! These tables are computer-generated, and a typical radio diary report may contain 100 or more pages of numbers.

 

 

 

 

Reach

 

The reach of a radio station, also known as cumulative audience is the number of different people who listen to a station in a time period longer than the basic unit. If the basic unit is a quarter-hour, then (because of the way diaries are filled in, as explained above) the reach for a quarter-hour is the same as the average. As the time period grows, the reach grows too, but m more and more slowly.

Let’s continue the example of the audience of 2,000 in one quarter-hour. Suppose the station was broadcasting a half-hour program at the time, and the other quarter-hour of the program had an audience of 2,500. Some listeners would have heard the whole program, while others would have listened only during the first quarter-hour or the second quarter-hour. If there had been a total change of audience halfway through the program, so that nobody listened to both quarter-hours, the reach would be 4,500, because that many different people would have listened to the program. At the other extreme, suppose that all 2,000 people who listened in the first quarter-hour also listened in the second quarter-hour. But because the audience in the second quarter-hour was 2,500, that means another 500 people must have switched on halfway through the program. Therefore, in this case, the reach was 2,500: the number of different people who listened to all or part of the program. So by knowing the two quarter-hour audiences, we can deduce that the reach must be somewhere between 2,500 and 4,500. But to get the actual reach, it needs to be calculated from the listening data for each respondent.

The same principle applies when extending reach from a half-hour, to a long time zone, to a full day, to a week. The longer the period, the larger the reach – but as the length of the time period grows, the reach grows more and more slowly. It can never go backwards – e.g. it’s impossible for a 7-day reach to be less than a 5-day reach. Also, because reach must be calculated from the listening records of individuals, the reach figure is limited by the length of the diary. You can’t calculate a one-month reach from a one-week diary, for example – because you don’t know how many people who didn’t listen to a station in that week might have listened in the next few weeks.

Like average audience, reach can be expressed either in estimate thousands of listeners, or as a percentage of the population. It tends to be expressed as thousands for shorter time periods, and as percentages for longer periods – e.g. “FM99 reaches 11,500 people from 7 to 10pm on Saturday night” or “39% of the total population in this area are reached by FM99 at least once a week.”

 

Share

 

Audience share is a different kind of measure altogether. Both average audience and reach are counts of people. Audience share, though always expressed as a percentage, is not a percentage of people, but of person-hours. It’s easy to forget this, but try not to! Take the statement “FM99 has a 40% share of the radio audience in this area.” That means: out of every 100 hours that people in the area spend listening to radio, FM99 has 40 of those hours. That does not mean it has a reach of 40%. The reach could be a lot more or (more likely) a lot less, depending on the number of stations in the area, and how long people spend listening to each station.

Think of it like this: if you add together the shares for all stations in an area, the total is always 100%. That’s why it’s called audience share. It can be calculated for a single quarter-hour, a time zone, a day, a week, or any time period. No matter how few people are listening to radio at a given time (e.g. 4 a.m, when audiences are usually tiny), the share for all stations will always add to 100%. (However, reach figures usually add to a lot more than 100%. If the total of all station’s reach figures is 200%, that means the average person listens to 2.00 stations in that time period.)

Share figures are useful for comparing different demographic groups. For example, if a radio station is trying to appeal to young people, it will probably have a much larger share of the under-30 audience than of the age 45-plus audience. Also, because radio audience sizes usually vary in a consistent pattern throughout the day, calculating a station’s share for each quarter-hour in the day can show which programs are strongest and weakest, compensating for the variations in total audience size.

 

Duration of listening

Duration is sometimes known as the average time spent listening, which describes it clearly. Consider a time zone audience, which might average 30% of the population. This can be expressed in another way, which is mathematically identical: if 30% of people are listening, on average, then it follows that the average person listens for 30% of the time. So if it was a 3-hour time zone, the average duration is 30% of 3 hours, which is 90% of an hour, or 54 minutes. I mentioned earlier that the average time spent listening to radio in Australia is about 3 hours a day. That’s a duration figure. It can be converted back to an average as follows: since there are 24 hours in a day, and the average person listens for 3 hours, the average audience is 3 out of 24, which is 1 out of 8, which is 12.5%. Therefore the average radio audience in Australia is 12.5% of the population. You can easily switch between these two figures, depending on which is more useful for the point you are making.

That’s the simple definition of duration, but often it’s more complicated that, because sometimes you want to exclude people who didn’t listen at all. That is, the above definition calculates an average of the whole population, but sometimes you want an average duration for those who actually listened. In that case, the average audience must be divided by the reach, then multiplied by the length of the time period. For example, about a fifth of the people in Australia don’t listen to radio at all on an average day.That means the all-station all-day reach is 80%, not 100%. if the average is 12.5% of all people, it must be 12.5/.8 of the actual listeners, or 15.625% of them. Therefore the duration (among those who actually listen) is 15.625% of 24 hours, or 3.75 hours.

 

Impressions

Impressions, also known as impacts is a measure used by advertisers. It’s the sum of the audiences at specified times – e.g. when ads are broadcast. If a station has an audience of 2,000 in one quarter-hour and 2,500 in the next, and the same ad is broadcast once in each quarter hour, that will be 4,500 impressions: the number of times the ad was heard, regardless of the number of different people who heard it. If the ad is broadcast twice in each quarter-hour instead of once, the number of impressions will be 9,000. If the total cost of advertising is divided by the total number of impressions, you can calculate the cost per thousand impressions. This is a measure that advertisers find useful when working out which stations to advertise with.

 

Frequency

Frequency is another measure used mainly in advertising. it’s an answer to the question “how often did listeners hear the ad?” If (continuing the previous example) an ad is broadcast twice in each of two quarter-hours, the frequency will range between 0 (because some people won’t have heard it at all) and 4 (among those who listened to the station for both quarter-hours). Actually, there are two measures of frequency: the average frequency and the frequency distribution. Frequency is normally based on the whole population – because that’s who the advertiser is trying to attract. If we know that the reach for the two quarter-hours was 3,000, and that there were 9,000 impressions (as above) the average frequency must be 3.

A full frequency distribution would show how many people heard the ad 4 times, 3 times, twice, once, and not at all. These figures cannot be calculated from the data I’ve supplied – you’d need to go back to the raw data. A common goal for advertisers is to achieve what they call a 3-plus reach – that is, the number of people who hear a message at least three times. The reasoning is that people don’t fully understand a message till they’ve heard it 3 times – which is one consequence of defining radio listening as being within earshot of an audible radio. If you used a tighter definition, you’d find that one hearing was often enough to be effective. The 3-plus rule of thumb is only a starting point. It is not well supported by research data.

 

Loyalty

If all listeners to a station listen only to that station, its loyalty is 100%. This is usually measured over one week: a standard cycle time in radio listening, both for programming and for survey samples. By definition, loyalty cannot be zero: listeners to a station must spend some time listening to it, otherwise they wouldn’t qualify as listeners. So the formula for loyalty to station A is:

(time spent listening to station A) divided (by time spent listening to all stations)

…usually expressed as a percentage. In an area with between about 5 and 20 stations available, a loyalty figure of 50% is on the high side. In other words, if the people who listen to your station at least once a week spend more time with your station than with all others combined, you are doing well. Unfortunately, because of the principle of double jeopardy that applies so widely to most consumption behaviour, the smaller the audience share your station gets, the smaller your loyalty is also likely to be. Statements such as “though we get a tiny audience, they are very loyal” are – unfortunately – hardly ever true. Occasionally, loyalty is called “share of ear”.

 

Other measures of audience

 

Those are the main measures of radio audiences, but others are sometimes used. One example is unduplicated reach – the number of people who heard a program or ad only once, even though it was broadcast several times.

Some audience measures can be done without a diary – e.g. the survey question “Which radio stations have you listened to in the last 7 days?” will usually produce a set of answers very similar to the weekly reach figures from a 7-day diary. However, audience share is much more difficult to estimate by simply asking people – but diary surveys are very expensive, and require complex software. By testing various question wordings, and comparing them with diary surveys, I found a question that closely approximates share figures without doing a diary: “Which one radio station do you listen to most often?” As with the share figures, the answers to this for all stations add to 100% – after you’ve ignored the people who can’t answer and those who insist on giving two answers. Results are usually within 2% of share figures from a diary survey, but slightly favour stations that people don’t spend much time listening to.