If a brand has a specific viewability goal, the best way to achieve this is by buying on what basis?

Buying on a vCPM (Viewable Cost Per Thousand Impressions) basis is the most effective way for a brand to achieve a specific viewability goal. This approach directly ties the cost to viewable impressions, meaning that the brand only pays for impressions that meet certain visibility criteria. With vCPM, the advertiser can ensure that their ads are actually seen by users, as it emphasizes the importance of impressions that are considered "viewable" according to established industry standards, typically defined by the Media Rating Council.

In contrast, CPM focuses solely on the number of ad impressions served regardless of whether they are viewable. CPC charges based on clicks, which does not guarantee that users even view the ad before clicking. Similarly, CPD is oriented around actions taken after ad exposure, such as downloads, and also does not ensure the visibility of the ads themselves. By choosing vCPM, a brand aligns its purchasing strategy with its viewability objectives, optimizing its spend to favor conditions that increase the likelihood of the ad being seen.