About counting discrepancies

Counting discrepancies occur whenever two or more parties are involved in the process. A common case is when a publisher integrates a third party script (agency script) in an insertion.

Discrepancies can occur with any metric used in online advertising: impressions, clicks, conversions etc. This article focuses on the investigation of impression counting discrepancies.

As a general rule, counting discrepancies of 10% or less are considered acceptable in the industry.


Here are some common causes of counting discprepancies:

  • the involved systems count at different points (different methodologies): e. g. one system counts an impression when the ad is requested, while the other system counts when the ad is delivered (client side impression)
  • short system outages leading to impressions not being logged
  • creatives are too heavy
  • page drop-offs: users leave the page before the creative was served (and counted) by the third party system
  • ad blocking software


Check if both systems implemented the cache busting macro. This macro is replaced by a random number upon each ad call. This changing random number makes each ad call unique, so that browsers will retrieve the ad from the ad server, rather than from its cache.

Check if both systems use the same timezone. Different timezones lead to different start and end date/time of the insertions (line items)

Creative Size
Check the weight of the creatives (kilobytes, megabytes). This may lead to latencies and less impressions counted on the third party side.

Date Range
Make sure the reports from both systems cover the same date range.

Frequency Capping
If the third party has specified a frequency capping, users who have reached the frequency cap will end up in empty delivery: our ad server will count an impression, but the third party does not return a response (thus, no impression is counted).

Targeting Criteria
Check if the third party has used targeting. Verify if these match with the targeting criteria you specified in your insertion(s).

A special case is when the same geo-targeting criteria have been used in both systems: the systems involved may use different geo-targeting technologies (vendors). These vendors may assign a user's IP adress to different geo-locations (geo-targeting is based on IP addresses).

For those using Google Analytics, make sure that you are using campaigns to effectively segment your referral traffic from other sources. Depending solely on the “referral” information that analytics provide isn’t reliable. Google provides a tool for building special URLs that track more accurately: https://support.google.com/analytics/answer/1033867?hl=en

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