The Company that You Keep: When to Buy a Competitor's Keyword
Search advertising refers to the practice where advertisers place their text-based advertisement on the search engine's result page along with the organic search results. With its growing importance, search advertising has seen a recent surge in academic interest. However, the literature has been ignoring some practical yet important problems of advertisers, including the keyword selection problem. In my dissertation, I focus on the keyword selection problem, more specifically, the choice of branded keywords in search advertising.
My dissertation begins with an observation on different patterns of branded keyword purchase behavior by the brand owner and its competitor. Under some branded keywords, we observe in the sponsored link, only the brand owner or only the competitor. However, under some other branded keywords, we observe both firms, or neither of them. Upon this phenomenon, I aim to understand what drives this puzzling pattern in a competitive environment. To this purpose, I develop a duopoly model where two firms compete in the product market with both horizontally and vertically differentiated products. Their products are evaluated by consumers whose perception is affected by what they see in search advertising. With this setup, Then I derive a subgame perfect equilibrium of the two stage game.
In a pricing equilibrium, I find that any benefit a firm gets from search advertising either due to exposure benefit or due to contrast or assimilation, helps this firm charge higher price while forcing the other firm charge lower price. This result affects the incentive for each firm to buy the branded keyword in the advertising stage. Specifically, firms have an incentive to buy the keyword only when the cost of advertising is justified by the exposure benefit but even in that case, each firm buys only when the detrimental context effect is not present. If the quality difference between the brand owner and the competitor is large and thus there exists a contrast between the two firms, the competitor with low quality product refrains from buying the keyword, because the contrast effect hurts the competitor. On the other hand, if the quality difference is small and thus two brands are assimilated, the brand owner with high quality product refuses to buy the keyword, because it is hurt by the assimilation effect. If the quality difference is in the intermediate range so that neither context effect is harmful to neither firm, both firms buy the keyword at the same time. On probing further the underlying incentives, I find that in some cases, the brand owner may buy its own keyword only to defend itself from the competitor's threat. In contrast, I also identify the case where the brand owner chooses to buy its own keyword and precludes the competitor from buying it. My result also suggests that both firms may be worse off by engaging in advertising, as in the prisoner's dilemma case.
On an extension, I provide an analysis on the impact of the insufficient advertising budget. If the budget is limited, both firms may have an incentive to hurt the other firm taking the higher slot, by increasing the bid amount and thus quickly exhausting the competitor's budget. The budget constraint also deprives the advertisers of the incentive to buy the keyword and thus, the budget-constrained advertisers may refuse to match the competitor's purchase of the keyword. Finally, the experimental investigation shows the existence of the exposure effect and the context effects. It also supports the model prediction based on estimated model parameters together with the empirical observation.
Raising Rivals' Cost
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