Radio and television are very different from magazines and newspapers when it comes to measuring the size of their audiences. Such media have no visible trace that they have been received. The program and the advertising message are often mixed, and it is difficult to divorce the two. There are four basic ways to measure the size of the audience for any radio and television program. Each of these is discussed briefly below.
Coincidental Method: This method is based on a sample of homes, using the telephone to solicit responses about what radio ad television programs are being listened to or viewed. Typically respondents are called and asked whether anyone in the home is listening to the radio or viewing television, and, if so, to what program and station they are tuned. The question is also asked: What is the name of the sponsor or product being advertised? Ratings are based on the percentage of radio or television homes tuned to a particular program. This method measures average audience on the assumption that calls are spread evenly throughout the time of the program.
This system has the advantage of speed and economy; nevertheless, it has severe limitations. First, the results may not be valid, since only homes with telephones are included. Even where network shows are concerned, it is usually not economically feasible to obtain a sample of rural homes. For these reasons, the total size of the audience cannot be estimated accurately.
A second difficulty is that such procedures do not produce any continuous information about the audience. One cannot tell how many homes are reached over a period of several programs that is, what the cumulative audience is. Nor can one tell what the total audience is for a given program at any one time, since no measure of tuning in or out is obtained.
A third major limitation is that calls must be limited to certain hours of the day and night, such as after 8:00 am and before 10:30 pm. Programs not included in this time span cannot usually be measured using the telephone coincidental method. There may also be a tendency on the part of some respondents to report they are viewing a more socially approved program than they are.
Roster Recall: This is a technique that consists of aided via personal interviews. The interviewing is done shortly after the particular time period (usually four hours) to be measured has been completed. A list or roster, of programs by quarter hours is used to aid respondents in remembering what programs were listened to or viewed.
The rating obtained by the use of the roster-recall method are dependent upon memory and are subject to inflation or deflation , as a result of the status, or lack of status, of certain programs. This is method’s biggest limitation, since the less popular shows tend to be discriminated against. Such a method does not provide any continuous information about the nature of the audience, nor does it permit measurement of the cumulative audience. Because respondents are queried about only a short time span, duplication analysis cannot be made. It is not estimate the number of persons who view program A and also program B unless both programs fall within the time span on which the respondent is being interviewed.
TV Meters: The use of electronic recorders (sometimes referred to as passive meters) that can be attached to a television set without interfering with its normal operation have been used by the A C Nielsen Company since the 1950s to monitor TV audiences. The machine records when the set is on and to what station it is tuned. All of this is keyed to time periods so that a continuous record is provided. Thus, the following data are reported:
1. Total audience – number and percent of television homes tuned to each program for a minimum of six minutes.
2. Average audience – equivalent to the number of television homes tuned to the full program (the average number of homes minute by minute).
3. Share of audience = Number of homes watching specific program / Numbers of homes watching any program at that time period.
Since the audiometer sample remains essentially the same from month to month, a measure of the cumulative audience can be obtained. In addition, elaborate duplication data can be studied, since data are available from over a long period. Data can be broken down by such household characteristics as region, city size, age of male head, total family income, and presence of children.
Despite the objectivity of such a system, it suffers in that it does not indicate whether a program is being viewed and, if so, by whom.