Though the campaign involved a national media buy, variation in exposure occurred due
to the presence or absence of local affiliates and cable markets for the networks airing the
advertisements (FOX, UPN and WB). Cumulative gross rating points (GRPs) for each of the 210
television markets in the United States provided measurement of student exposure to the
campaign. (GRP is reach times frequency, which includes the percentage of the audience
exposed and the number of times they are exposed to the advertising.) The variation over the
two-year period evaluated was from 3,867 GRPs to 20,367 GRPs and the analysis included preexposure
survey results where the GRPs were zero (Farrelly et al. 2005). This technique of