In some cases, you may find that the number of ad requests is higher than the number of ad impressions. This article provides some of the most common causes for this type of discrepancy.
Please study the article about "what is the difference between an ad request and an ad impression?" first.
It is not uncommon for site visitors to click on a link to move to a new page or a different site before all the ads on a page have completed loading. This will result in a situation where the ad requests have already happened, and have been counted, but not all ad impressions. The reason is that an ad impression will only be counted when the banner has actually been delivered to the browser.
Most commonly seen with video ads, there may also be a situation where a web page or video player sends a request to the ad server for it to select a banner. However, when the site visitor does not engage with the video content (for example does not click the Play button), the video ad is never played and thus an impression will not be counted.
Delivery rules (targeting)
When a web page calls a zone that doesn't have at least one banner with linked to it that has no delivery rules, the ad server will return an empty result set. The effect is that a request will be counted and a blank impression.
In case the web developer is using Revive Adserver's single page call, the cause of a discrepancy can be that the 'head' of the page sends a call for all known zones of a website to the ad server, but the page itself only displays a subset of these zones. The effect is that an ad request will be counted on the zones that are part of the 'head' call, but those zones will obviously never have an impression.