We focus upon the form of advertising referred to as "banner ads" and "target ads." This primitive form of Web-based advertising may ultimately not be the most effective, but as the current dominant form, we feel it is appropriate to propose a set of standards for its measurement. At a minimum, using banner and target ads, whatever the limitations might turn out to be, provides a concrete example to work with. Although we expect Web-based advertising efforts to evolve, the problem with making recommendations more general so that they could encompass other types of yet to be developed Web-based advertising is that they would be too broad and diffuse to be practically useful. A banner ad is a small, typically rectangular, graphic image which is linked to a target ad . Banner ads come in a variety of sizes, with 90 percent of banner ads ranging from 120 to 500 pixels wide (with a median of 460 pixels) and from 45 to 120 pixels high (with a median of 60 pixels) (Focalink 1996). Banner ads typically provide little information other than the identification of the sponsor, and serve as an invitation for the visitor to click on the banner to learn more. Following are a few examples of banner ads: [ads not shown here] Target ads, on the other hand, can be fairly involved, ranging from a single web page with basic HTML, to a Web page enhanced by Java applets, audio, or forms, to a series of linked pages, or to a complete corporate "Internet Presence," "Content," or "Online Storefront" site (Hoffman, Novak & Chatterjee 1995). Chatterjee (1996) considers banner ads to be a form of passive advertising exposure, in that the consumer does not consciously decide to view the banner ad. Rather, the banner ad is presented as an outcome of accessing a particular Web content page, or as the outcome of entering a series of key words into a search engine. Conventional market segmentation theory would lead us to predict that the more targeted the banner ad, the higher the click rate. Thus, ads placed on home pages of general-interest sites, or on the entry page of a search engine would have lower click rates than ads that are consistent with the content of a narrowly targeted web site, or banner ads presented by a search engine in response to specific keywords (e.g. ads for Lionel trains presented every time a visitor searches for "model railroad" or for "Neil Young"). Paid links are a different form of passive advertising, and may be most simply viewed as a text version of a banner ad. Paid links are often incorporated in directories, which may contain large numbers of such paid links.