estimated 109.6 million television households in the United States. Thus, a single national ratings point represents 1%, or 1,096,000 television households for the 2004–05 season. When used for the broadcast of a program, the average rating across the duration of the show is typically given. Ratings points are often used for specific demographics rather than just households. For example, a ratings point among the key 18- to 49-year-olds demographic is equivalent to 1% of all 18- to 49-year-olds in the country. A Rtg/TVR is different from a share point in that it is the percentage of all possible households, while a share point is 1% of all households watching television at the time. Hence the share of a broadcast is often significantly higher than the rating, especially at times when overall TV viewing is low. A low TRP can have an adverse effect on a TV program eventually leading to its closure. GRPs/TRPs Gross rating points (GRPs) or target rating points (TRPs) are chiefly used to measure the performance of TV-based advertising campaigns, and are the sum of the TVRs of each commercial spot within the campaign. An ad campaign might require a certain number of GRPs among a particular demographic across the duration of the campaign. The GRP of a campaign is equal to the percentage of people who saw, multiplied by the average number of spots that these viewers saw. Targeted Rating Points are a refinement of GRPs to express the reach time frequency of only the most likely prospects. For example, if a campaign buys 150 GRPs for a television spot, but only half of that audience is actually in the market for the campaign's product, then the TRP would be stated as 75 to calculate the net effective buy . Gross rating point, a standard measure in advertising, it measures advertising impact. It is a percent of the target market reached multiplied by the exposure frequency. Thus, a program which advertises to 30% of the target market and gives them 4 exposures, will have 120 GRP. GRPs as a measure has some limitations. People like to think of it as a measure of impact, but that is really overstated. Impact should measure sales; this measures exposures, which is in fact assumed not actual exposures. Basics of TAM (television advertising measurement): Universe: Universe is the total or actual number of people in a defined target audience. Reach: