Google admit advertisers wasted their money on more than 50% of Internet ads
qz.com
qz.com
I don't understand the issue here. Unless things have changed over the years, the vast majority of Google advertisers would be paying "per click" (CPC) rather than "per impression" (CPM). When I was advertising it was quite difficult to pay on a "per impression" basis, and the offers to enable this were after considerable data had been calculated using the "per click" method. Switching to "per impression" was optional and appeared to average your existing "per click" spend rather than some program to hide your underlying click spend.
As a "per click" advertiser I don't care if my ad is only "in view" half the time it's displayed. I care that a person is clicking and they intended to click.