ارزشمندی تبلیغات آنلاین

Sending general advertisements with inflationary claims may attract additional visitors with whom an advertiser is poorly matched. This is costly when ads are priced per-click because many visitors (clickers) will not purchase. This renders per-click advertising particularly conducive to the transmission of information via ads. The admissibility of information transmission depends not only on advertiser behaviour, but also upon consumers' interpretation of and trust in ads. In less conducive environments, consumers quickly learn to place little stock in the claims they see advertised. This mechanism undermines the ability of advertisers and consumers to communicate under per-impression or per-sale fee structures. Consumers benefit from increased informativeness, but distortions introduced by the market power given to advertisers imply that society may be better-off with no information transmission taking place.

I investigate the role played by the prevailing fee structure in determining whether advertisers and consumers are able to communicate and the extent to which information about products can be transmitted via advertisements. At the core of these results is the following simple idea: a per-click advertising fee can serve as a disincentive to sending uninformative advertisements of general appeal by making it costly for an advertiser to attract visits from consumers with whom it is poorly matched. By contrast, since a sale to a poorly matched consumer is as good as one to anyone else, firms that pay for ads on a per-sale basis have an incentive to attract a visit from any consumer that will purchase with positive probability. Likewise, once a consumer is shown an ad, the cost of that impression is sunk and firms that pay per-impression are incentivised to attract any consumer with some positive probability of purchase. This incentive causes advertiser–consumer communication to break down and undermines the existence of fully-informative equilibria. The usefulness of advertisements is then reduced and consumer welfare is harmed. However, for some specifications of search costs, reduced ad information content is beneficial for publishers and society as a whole.

Charging advertisers on a per-click basis provides a disincentive to attracting poorly matched consumers, and can therefore encourage the transmission of informative advertisements. Conversely, advertisers who pay for advertisements on a per-impression basis, or pay only in the event of a sale find attracting visits from poorly matched consumers to be profitable provided that those consumers will buy with some positive probability—however small that probability is. Such fee structures are therefore much less conducive to the equilibrium transmission of information. A key message of this work is that the informative capacity of advertisements depends as much upon consumers' interpretation of (and trust in) ads as on the ad messages themselves. Crucially, it is precisely when advertisers wish to inflate their own click-through rate that they are most unable to do so because consumers anticipate this adverse incentive and adjust their response to ad messages accordingly. Consumers benefit from improved transparency but the effect of improved information transmission on publisher profits and social welfare is ambiguous. When there are many advertisers competing for the advertising resource, the auction mechanism does a good enough job of selecting advertiser to mitigate the effects of reduced information transmission. Under such circumstances, pay-per-impression and pay-per-click are welfare equivalent, whilst pay-per-sale delivers consistently lower welfare owing to the distortionary effects of a marginal tax on firm sales.