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In-Depth Information
(1) The position of the ad in a list has great influence on whether or not it is clicked. The
first on the list has by far the highest probability, and the probability drops off expo-
nentially as the position increases.
(2) The ad may have attractiveness that depends on the query terms. For example, an ad
for a used convertible would be more attractive if the search query includes the term
“convertible,” even though it might be a valid response to queries that look for that
make of car, without specifying whether or not a convertible is wanted.
(3) All ads deserve the opportunity to be shown until their click probability can be approx-
imated closely. If we start all ads out with a click probability of 0, we shall never show
them and thus never learn whether or not they are attractive ads.
8.1.3
Issues for Display Ads
This form of advertising on the Web most resembles advertising in traditional media. An ad
for a Chevrolet run in the pages of the New York Times is a display ad, and its effectiveness
is limited. It may be seen by many people, but most of them are not interested in buying
a car, just bought a car, don't drive, or have another good reason to ignore the ad. Yet the
cost of printing the ad was still borne by the newspaper and hence by the advertiser. An
impression of a similar ad on the Yahoo! home page is going to be relatively ineffective for
essentially the same reason. The fee for placing such an ad is typically a fraction of a cent
per impression.
The response of traditional media to this lack of focus was to create newspapers or
magazines for special interests. If you are a manufacturer of golf clubs, running your ad
in Golf Digest would give you an order-of-magnitude increase in the probability that the
person seeing your ad would be interested in it. This phenomenon explains the existence
of many specialized, low-circulation magazines. They are able to charge much more per
impression for an ad than is a general-purpose outlet such as a daily newspaper. The same
phenomenon appears on the Web. An ad for golf clubs on sports.yahoo.com/golf
has much more value per impression than does the same ad on the Yahoo! home page or an
ad for Chevrolets on the Yahoo! golf page.
However, the Web offers an opportunity to tailor display ads in a way that hardcopy
media cannot: it is possible to use information about the user to determine which ad they
should be shown, regardless of what page they are looking at. If it is known that Sally likes
golf, then it makes sense to show her an ad for golf clubs, regardless of what page she is
looking at. We could determine Sally's love for golf in various ways:
(1) She may belong to a golf-related group on Facebook.
(2) She may mention “golf” frequently in emails posted on her gmail account.
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