Ad server discrepancy
When an ad server serves ads that are hosted by a third party, small reporting discrepancies between the two systems may occur. For example, the publisher's ad server will count the impression initially, then the third party will count the impression after the ad is returned. Discrepancies may also result from:* Different definitions: Publishers count the ad request and advertisers count the ad displayed.
* Large creatives: Large creatives can have long load times and introduce differences in impression counts.
* Latency: Any lag in the connection between the ad request and the displaying of the ad can create differences in counts; the user may navigate away before seeing the advertisement or the advertiser's landing page.
* Network connection and server reliability: An ad server may fail briefly, not receive a connection, or encounter an issue while logging a request, which results in different counts.
* Timing differences: Ad servers may operate on different time intervals or geographic time zones, which results in temporal differences.
* Ad blockers: Publishers issue an ad request, but the ad is prevented from being displayed by an ad blocker.
* Caching: A creative may be cached in the browser or on a proxy server; no ad request is seen by the advertiser server, which results in impression count differences.
* Spam filtering: Ad servers may filter out spam impressions and clicks, impressions from robots and spiders, back-to-back clicks, and other activities. These filtering technologies are implemented in different ways; some servers may be more or less aggressive in their filtering, which results in spam and click count differences.
* Trafficking errors: An ad tag may be implemented incorrectly so that one ad server is able to see the impressions and clicks while another server doesn't (or only receives a subset of the statistics).
* Frequency capping: An advertiser's frequency cap could prevent an ad request from being filled, which may cause different impression counts.
