View-through conversions correspond to people that converted after viewing an ad without having clicked the ad itself. The view-trough conversion rate is then the percentage of people who view an ad without cliking it and later complete the conversion action.
View-trough conversion measurement is important for determining campaign effectiveness, notably for branding campaign. It is a way to show that the 99,8% percent of persons who don’t click are not a total waste of money.
Most marketing vendors - ad exchanges, ad networks, retargeters, ESP - offer their clients to implement a provided conversion tracking code. Retargeters are especially emphasizing view-trough conversions.
Most often, the view-trough conversion is counted when it happens within 30 days after the user saw, but did not click, the ad.
View-through conversions are tracked via cookies that are placed on users’ computers when the ad is served and via a conversion tracking code provided by the marketing vendor and placed on conversion pages.
View trough conversions are often overestimated for large campaigns when they are counted by the marketing vendor’s tracking tag, as the conversions may have been caused by other offline or online marketing campaigns.
View-trough conversions are theoritically better estimated with advertisers’ attribution models. But even in this case, the measurement is complex and quite often offline marketing campaigns are not taken into account.
An example of view-trough conversions reporting in AdWords platform for content network retargeting campaigns: