We've rolled out a change in the way we count impressions. The change is reasonably simple, as illustrated below.
So basically we're counting the impression at the end of delivery rather than at the beginning. For most publishers, this won't make a big difference in terms of impressions, but you may see lower impression counts. This will mostly happen on pages where the user clicks through the page before the ad has time to load.
From a revenue standpoint there are two things to look at:
- CPC ads: Nobody clicks on ads they haven't seen, so you're not losing any click revenue.
- CPM ads: One of the drivers for this change is that our partners are reporting that our impressions counts are too high. This change is expected to bring the numbers in line. We're not anticipating any large change in payouts here, just happier advertising partners. Most CPM campaigns are capped per user and most users are reaching their caps.
On a related note, impression counts for today (2008-12-17) will be low. This is a side-effect of the changes we made, overall revenue should remain reasonably stable, expect these numbers to line up again tomorrow.