Measurement Foundations: Calculating GRPs/TRPs?

What is a GRP/TRP?

GRPs/TRPs are a way to quantify the number of exposures (which are impressions) as a gross percentage of a specific population.

Calculating GRPs &TRPs

Calculating a GRP/TRP is a simple formula that takes the universe impressions and divides it by the universe population. One rating point represents impressions equal to 1% of the selected population.

GRPs/TRPs can be greater than 100% because just like impressions, GRPs/TRPs account for duplication of exposures. GRPs and TRPs can be added across OOH formats as well as other media, as long as the universe base is the same. This allows clients to compare and evaluate the media weight of a campaign in a standardized way.

Why Use Them?

• Serve as a shorthand measure of the total amount of exposures, and advertisers use this metric more often than even impressions.
• Allow advertisers to understand the media weight across markets as a standard representation of that market's universe.
• Provide a known, fundamental, derivable measure of advertising weight bought, and they allow that weight to be compared across different types of media.
• Used by planners and advertisers to develop budgets and as the foundation for communication goals.
• Serve as the basis for most media's cost parameters.

THINGS TO REMEMBER:

• Gross Ratings Points and Impressions are interrelated.
• Impressions are the number of times an ad has been exposed to a universe and GRPs/TRPs converts those impressions to a percent of the universe you are analyzing. 
• Remember that the universe is the population of the group being measured and needs to be identified prior to evaluating all metrics.

If you have any questions or comments, please reach out to geeokout@geopath.org!