Show rate
The percentage of returned ads that were displayed in the app to the user. It's calculated by dividing impressions by matched requests:
Impressions / Matched requests
For example, if the total number of Matched requests is 80, but your app only shows 60 of these, then the app’s Show rate will be 75%.
To view the show rate for each ad network, select Ad source in the Dimensions field at the top of your AdMob Network report.