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                                    Yahoo! Search Marketing

                                       Click Measurement Process
                                                    Description of Methodology

                                                                Effective 29 May 2009

                                                                        Yahoo! Inc.
                                                                     701 First Avenue
                                                                  Sunnyvale CA 94089
Description of Methodology

        This Description of Methodology (DOM) is a summary of the click measurement process
        employed by Yahoo! Search Marketing (YSM). It includes a general description of the click
        measurement methodology, filtration processes, and reporting procedures.

Yahoo! Search Marketing Click Measurement Audit Process
        This section describes what is and is not incuded in the Yahoo! Search Marketing Click
        Measurement Audit Process.

Components Included in the Click Measurement Audit Process
        The Click Measurement Audit Process evaluates the Yahoo! Search Marketing click
        referral cycle, serving systems, data pipeline, click filtration, and reporting technology. The
        following click measurement components are included in the audit process:
        • Click Measurement Methodology (see Click Measurement Methodology Overview)
        • Serving systems: Sponsored Search, Content Match, and Domain Match, (see Click
          Measurement and Serving)
        • Click event data collection from the serving systems, (see Data Collection)
        • Click filtration using click-through protection system (CPS) technology (see Click Fil-
          tration Methodology)
        • External reporting processes (see External Data Reporting)

Components Not Included in the Click Measurement Audit Process
        The Click Measurement Audit Process does not include systems or processes that are
        outside Yahoo! Search Marketing, or that are not directly related to click measurement.

Click Measurement Methodology Overview
        This section provides a general description of the click measurement processes used by
        Yahoo! Search Marketing.
        Yahoo! Search Marketing systems measure clicks according to the methodology, approved
        by the Interactive Advertising Bureau (IAB), called the multiple-click-per-impression
        method. Click counting measurements are filtered for robotic and invalid click activity in
        accordance with the provisions of the IAB Click Measurement Guidelines.

                                © 2009 Yahoo! All Rights Reserved.
                     Yahoo! Search Marketing Click Measurement Process—Description of Methodology

         Click measurement and the management of clicks are based on actual measurement. All
         clicks are counted; there are no statistical projections or estimates.

Click Methodology Phases
         Yahoo! Search Marketing considers a click valid if it meets all of the following criteria:
         • It is a click on an advertiser’s ad (ad title),
         • The user has been redirected to the advertiser’s page (HTTP 302 redirect), and
         • The click has undergone click filtration steps (as described in this document).

Click Type
         The IAB Guidelines define the Click Referral Cycle in four phases: initiated click,
         measured click, received click, and resolved click. Yahoo! Search Marketing counts and
         manages a click at the measured click phase. A click is recorded when Yahoo! Search
         Marketing has sent the user an HTTP 302 redirect to the advertiser landing page or Web
         There are limitations to absolute counting accuracy depending on the specific
         measurement trigger that is being used. For example, latency can result in a 302 being
         counted even if the user abandons the transaction before arriving at the landing page.

Multiple-Click-Per-Impression Method
         The IAB Guidelines define two valid click counting methods: one-click-per-impression
         and multiple-click-per-impression. Yahoo! Search Marketing proprietary technology uses
         the multiple-click-per-impression method to collect and record clicks. Yahoo! Search
         Marketing allows multiple clicks per ad impression, and therefore click-through rates
         greater than 100% can occur.
         The Yahoo! Search Marketing multiple-click-per-impression process uses the following
         • Yahoo! Search Marketing tracks all clicks logged by our click measurement servers and
           uses a defined repeat click refractory period rule to prevent navigational mistakes. A
           click is considered valid when the time between the click and the previous click on the
           ad impression is greater than the amount of the repeat click refractory period.
         • Yahoo! Search Marketing also uses a defined impression-staleness-window. A click is
           considered valid when the time between the ad impression and the click is less than the

Click Measurement and Serving
         Yahoo! Search Marketing measures clicks that are enabled by three different serving
         systems: Content Match, Sponsored Search, and Domain Match.

iii                               © 2009 Yahoo! All Rights Reserved.
                  Yahoo! Search Marketing Click Measurement Process—Description of Methodology

       • Content Match™ is a Yahoo! Search Marketing serving technology that allows pub-
         lishers to display contextual ads in their served Web pages. When a user browses to a
         Web page, the publisher-side implementation sends an HTTP request to Content
         Match. The request provides instructions regarding the context of the serving site.
         Content Match matches advertiser ads to the context and returns those ads to the user
         for display in the publisher’s Web page. When the user clicks on a displayed ad, Con-
         tent Match executes an HTTP 302 redirect.
       • Sponsored Search™ is a Yahoo! Search Marketing serving technology that serves
         paid, ranked ads. Sponsored Search selects ads for serving based on:
          – the search string entered on a search engine query page, or
          – a string mapped to by the publisher based on a user search string entered on a
                search engine query page, or
          – a directed search, in which a search query is formed automatically based on the
                navigation path (also referred to as “breadcrumbs”) on the user page.
       • Domain Match™ is a Yahoo! Search Marketing serving technology that finds term
         suggestions (topics) and sponsored (advertiser) ads most relevant to undeveloped
         domain names, unregistered domain names, and other unresolvable URL strings that
         users type into the Web browser address field. When received, Domain Match decodes
         the search query and forwards the query to Sponsored Search for serving. Domain
         Match relates to advertisements displayed on the pages of a particular domain, where
         the domain name itself is analogous to a search query (such as For
         this reason, Domain Match is part of the Yahoo! Sponsored Search marketplace.

Data Collection
       Click data is managed and monitored by a data pipeline that is referred to as “Panama.”
       This data pipeline is composed of a data logging system, a data store, a file-based data
       warehouse, and a data mart that supports reporting and auditing.
       The initial input to the full Panama data pipeline includes the impression and click events
       from the serving systems.
       The Panama data pipeline aggregates and summarizes the data logs for reporting and
       checks for errors. Retrieval and processing procedures are fully automated and designed
       for a low likelihood of collection and aggregation errors. The collection and aggregation
       processes have several checks and balances to ensure protection against lost data and
       There are several data elements collected in the Panama data pipeline. The following are
       some examples of the data collected:
       • IP Address: Internet Protocol (IP) Address represents the address of the user making
         the request. An IP address is used primarily for determining the geographical location
         of the user and for segregating the traffic originating from within the Yahoo! internal
       • Cookie Values: Used to uniquely identify users.

iv                            © 2009 Yahoo! All Rights Reserved.
                    Yahoo! Search Marketing Click Measurement Process—Description of Methodology

         • Date/Time: Date and time of the click and serve events logged by Yahoo! Search
           Marketing servers.
         • User Agent: Text string, provided by the browser, containing information, such as
           type and version about the browser that queries the site. This may also contain terms
           that can help identify traffic from non-humans (robots, spiders, crawlers, or agents).
         • HTTP Referrer: Text string that contains the address (URL) of the resource from
           which the request-URL was obtained.

Click Filtration Methodology
         This section describes the filtration methodology used to manage quality of clicks. Click
         Filtration is a critical step in managing traffic quality. Yahoo! Search Marketing employs
         tools, macros, filters, and processes that analyze traffic patterns in order to isolate and
         evaluate unusual activity. Unusual activity may or may not indicate invalid click activity.

Click Filtration and the Click Protection System
         Yahoo! Search Marketing uses the Click Protection System (CPS) to achieve Click
         Filtration. CPS determines whether clicks are valid (billable to the advertiser) or invalid
         (not billable to the advertiser). The goal of CPS is to be as accurate as possible in refraining
         from billing for clicks that occur due to abuse, naive navigation, redundant user behavior,
         or other unusual click activity, and therefore to bill only for those clicks that represent
         incremental economic benefit to the advertiser.

Click Filtration Process Flow
         CPS receives data via the Panama data pipeline, described in the Data Collection section of
         this document. It then validates, analyzes, and classifies clicks as billable or unbillable in
         the data pipeline. Clicks that are not billable are marked as invalid, and relevant
         downstream business systems are provided with that information.

Click Filtration and Validation Parameters
         CPS filters are comprised of numerous complex and proprietary techniques to detect and
         filter invalid traffic as defined in the IAB Guidelines. Filtration parameters include, but are
         not limited to, the following:
         • “Bad” sources. CPS discards clicks from invalid URLs, locations, or browser types.
           These include, but are not limited to:
            – Clicks that originate from robots as designated in the IAB/ABCe International
                Spiders & Robots List.
            – Clicks that originate from browser types that are not considered valid by the IAB.
                The list of valid browsers is included in the IAB/ABCe International Spider &
                Robot List.

v                                © 2009 Yahoo! All Rights Reserved.
                    Yahoo! Search Marketing Click Measurement Process—Description of Methodology

             –    Clicks that originate from browser types that are not considered valid by Yahoo!
                  Search Marketing. Yahoo! Search Marketing keeps an internal list of blacklisted
                  user agents.
         • Repeat clicks. CPS flags as invalid repeat clicks from the same sources when the num-
           ber of repeat clicks exceeds certain thresholds.
         • User cookies. Yahoo! Search Marketing uses cookies to uniquely identify users, then
           keeps a database of users who are known to generate click spam. CPS can then filter
           the click's cookie-based user ID.
         • Robot exclusion. Yahoo! Search Marketing Web servers include a robots.txt file
           that disallows all robots.
         • Caching. To prevent caching, the Yahoo! Search Marketing Web server checks for an
           HTTP prefetch header and, if found, blocks those prefetches using a 403 denied
           return code.
         • User agents. Per the HTTP standard, when a client initiates a request, the client uses a
           user agent string to identify itself. Yahoo! Search Marketing has developed rules that
           define acceptable or valid user agent strings.
         • Block list. Yahoo! Search Marketing maintains a list of, and eliminates clicks from, cer-
           tain IP addresses, including Yahoo! internal IP addresses.
         • Click and impression. To be considered valid, a click must be associated with an
           impression and must occur within a reasonable amount of time after the impression
           was served.
         • HTTP Referrer. A referrer is the address (URL) of the resource from which the
           request URL was obtained. Yahoo! Search Marketing has developed rules that define
           acceptable or valid HTTP referrers.
         • Publisher testing. Publishers are instructed to use publisher tags (source tags) ending
           in “test” to identify this kind of traffic. All clicks with source tags ending in “test” are
           flagged as invalid.

Activity-based Filtration and Analyses
         Yahoo! Search Marketing CPS algorithms perform pattern analyses that indicate
         suspicious click activity. In addition, analyses may be performed post-filtration, when
         Yahoo! Search Marketing performs regular monitoring of traffic and CPS to ensure proper

External Data Reporting
         Yahoo! Search Marketing provides advertiser reports using the Panama data pipeline
         advertiser-facing applications. These applications include a UI-based application and a

vi                              © 2009 Yahoo! All Rights Reserved.
                    Yahoo! Search Marketing Click Measurement Process—Description of Methodology

         Web-based programmer API application that provide several types of performance

Yahoo! Search Marketing Performance Reports
         Yahoo! Search Marketing performance reports contain both click and impression data.
         Performance information is based, in part, on the click-through rate using a formula of:
             Valid Clicks ÷ Impressions

         for the specific ad. Yahoo! Search Marketing performance reports are available for
         Sponsored Search (which includes Domain Match data) and Content Match serving
         systems. Yahoo! Search Marketing performance reports are based on the in-market local
         time zone for the advertiser account.
         There are several types of Yahoo! Search Marketing performance reports. Examples
         • Performance Summary Reports - Summary performance information for a campaign.
         • Daily Performance Reports - Daily summary performance information for a cam-
         • Keyword Performance Reports - Summary of performance for a keyword or set of

Discarded Clicks Report
         Yahoo! Search Marketing provides advertisers with a report that separates clicks based on
         billed clicks and discarded clicks. This report also shows the Invalid Click Rate, which is
         computed as
             the number of invalid clicks /(total number of valid and invalid clicks) * 100

Report Data Correction
         Yahoo! Search Marketing has a defined bug reporting and tracking process, as well as
         technical support, to retract and/or correct data that is reported to external users via the
         advertiser applications.

vii                             © 2009 Yahoo! All Rights Reserved.