In this advertisement, Jessica Simspon has been the face of Proactive (a skin care product) for the past several years and has helped launch and increase the sales of the product.
It has been proven that advertisements with celebrity spokespersons have a greater success as they show higher scores in believability and purchase intentions compared to advertisements with non-celebrities (Atkin & Block, 1983). The general belief among advertisers is that advertising messages delivered by celebrities produce a more important degree of interest, attention and often, better message recall than those delivered by non-celebrities (Cooper, 1984). This is a strategy known as the high status-admirer altercast, which would account for high demands of the products sold.
Thus, in this advertisement, individuals who admire Jessica Simpson and want to have the same quality skin as she has will be more prone to buy the product she endorses.
A few studies have compared celebrity advertising to non-celebrity ones. For instance, Friedman, Termini, and Washington (1977) did an experiment using celebrities and non-celebrities in an advertisement for a fictitious brand. They found that the celebrity version had higher scores on believability and item purchase compared to the non-celebrity one.
Atkin, C., & Block, M. (1983). Effectiveness of celebrity endorsers. Journal of advertising research, 23, 57-62.
Cooper, M. (1984). Can celebrities really sell products? Marketing and media decisions, 19, 64-65.