Let's say you're A/B testing book titles. All the book titles use the same metadata/description and keywords, but the only thing that changes is the title.
Why would you only get 1,000 impressions for one ad and 10,000 impressions for the second ad? It obviously has nothing to do with keywords/relevance, since both are the same?
Now let's say the 1,000 impression ad got a CTR of 15% and the 10,000 impression ad got a CTR of 7%. Which one is better? How would you interpret this, given that keywords/descriptions are all the same?