Video campaign up and running, check! Now how’s it doing? Holly has just a few minutes to pull some data together on how her audience is responding to the ads. In particular, she wants to know how well her ads are resonating — whether viewers are interacting with the ads they see. What metric should she investigate in AdWords Reporting?

Clickthrough rate (CTR)
Viewthrough rate
Cost-per-view (CPV)
View rate

Correct answer is:

Viewthrough rate

Explanation: View Through Rate (VTR) is the number of completed views of a skippable ad over the number of initial impressions.
VTR = Complete views (user did not skip) / Impressions (ad rendered)
Read more here: https://support.google.com/adxbuyer/answer/2961338