[maccam94]

As of today, some ads pay per click (CPC), but most ad spots pay per 1000 views (CPM). Ads can influence behavior after they are viewed, regardless of whether the user decides to interact with the ad. I'm sure Google has put tons of effort into trying to tie ad views to purchases, both online and offline (I bet GMail and Google Pay are leveraged for this).

I am not claiming this is good or bad, but clicks are not a good enough signal of efficacy for the vast majority of ads shown on the internet.

[cestith]

A good ad network's JS should be able to tell how long the ad was in the viewing portal, or for a video interstitial how long it played before the viewer skipped the end. That sort of signal could be useful, especially the way many sites use horizontal ad banners like horizontal rules in the pages.