Impression Count Deduplication

Impression duplication occurs when the mechanism used to track the impression is triggered multiple times. This can be caused by duplicated calls such as a page reload, or another type of user action that reloads/replays/retriggers the impression counting mechanism.

  • For Display, impressions are counted based on either each fetch for the impression, or else each pixel event that confirms an impression reached the user device.

  • For Video, impressions are counted based on markup within the VAST file that is triggered by the player when the video starts to play.

  • You can read more about these in the Impression Delivery and Tracking section.

Duplicated impressions need to be discounted from figures when measuring the effectiveness of a campaign, calculating discrepancy rates, billing, or any other metrics reliant upon impression count. This is to ensure you are using a more accurate figure for the amount of valid impressions served.

Identifying Duplicated Counts

To identify duplicated impression counts, you should base it on the impression ID present in your logs and discard all counts except for the least recent one, i.e the original impression. The impression ID is passed in the Bid Request field.

If you wish to use the Bid ID (Bid Request root id field) as the base for impression deduplication, you should use it in conjunction with the Impression ID field ( as there may be several impressions (ad slots) in a single bid request that come from different placements and are thus not duplicates.


It is important to deduplicate in the same way as BidSwitch to avoid any discrepancies.

Deduplication in BidSwitch