Radio or TV impacts expressed as a percentage of the population being measured. One rating point equals one per cent of the population. The population measured can be all people or any demographic group.
GRPs are a sum of all rating points over a specific time period or over the course of a media plan. The rating of a show represents the percentage of people (or households) tuned in to a television program as compared to the number of television sets in the particular television universe (geographical location). Each rating point is equal to 1%. If a show has a rating of 7, that means that 7% of all persons (or households) who have a TV were tuned in to that show (whether the other televisions were turned on or not). If there are two shows on a particular station during a particular time period, and the first show has a rating of 7 and the other a rating of 10, then the GRPs for that time period equal 17.
Media planners use gross rating points as a method of designing a media schedule in an attempt to deliver a maximum number of GRPs at minimum cost. In this instance, GRPs are calculated by multiplying the total reach (the unduplicated audience) of the schedule by the frequency (average amount of exposures) of the insertion in the proposed schedule. The gross rating points then will represent the product of reach and frequency and will express the “gross” duplicated percentage of audience that will be reached by the proposed plan. (It is important to note that GRPs are a percentage. Therefore, if a given market has 1000 TV households, each GRP represents 10 viewing households, whereas in a market of 10,000 TV households, each GRP represents 100 viewing households. Thus, the largest amount of GRPs does not necessarily mean the largest audience.)