DIFFERENCE BETWEEN TRP’s & GRP’s

Avoid expecting TRPs and GRPs to do more than what they actually do. That your commercial aired on a show does not mean that everyone watching the show actually saw the spot. Some viewers may have been preoccupied with other activities. Moreover, these metrics ignore audience engagement — the extent to which viewers pay attention to advertising content. With the growing popularity of online advertising for more precise audience targeting, many advertisers are wary of TRP and GRP metrics for this medium.
The aggregate total (the sum) of the ratings is called Gross Rating Points or GRPs. The sum of the ratings of a specific demographic segment may be called Target Audience GRPs or more simply TRPs. The term GRPs is generic and may refer to household GRPs or to specific target segment GRPs.
TRPs are a refinement of gross rating points, or GRPs. GRPs relate to the “total audience” exposure to advertising messages, whereas TRPs relate to the “target audience” exposure. The target audience, therefore, would be the percentage of the total audience tuned to that show who are most likely to buy your product or service.
Each GRP equals 1 percent of the total audience; a TRP equals 1 percent of the target audience. If 40 percent of total TV households saw your commercial one time, that would translate into 40 GRPs. If your target audience was 50 percent of the total audience, that would translate into 20 TRPs. Thus, GRPs and TRPs inform about the quantity of media weights, but not the quality of the weights.
Reach is the number or percent of different homes or persons exposed at least once to an advertising schedule over a specific period of time. Reach, then, excludes duplication.
Frequency is the number of times that the average household or person is exposed to the schedule among those persons reached in the specific period of time. Because it is an average frequency, dispersion of frequency of exposure will differ between specific schedules and daypart mixes.
GRPs, reach, and frequency are mathematically related in the following ways:
GRPs = Reach X Frequency
Reach = GRPs / Frequency
Frequency = GRPs / Reach