First of all a quick run through of the mobile ad industry jargon:
Requests - How many times an app requests an advert from an ad provider.
Impressions - The number of ads actually shown to users.
Fill rate - The percentage of impressions compared to requests.
Click Through Rate (CTR) - Percentage of impressions that result in a click.
Estimated cost per thousand impressions (eCPM) - How much an advertiser will be charged for 1000 advert impressions or how much a publisher will be paid for 1000 impressions.
For the past six months I have been earning money by showing adverts in my game "Cherry Chaser". I began with the refresh rate (recommended by Google) of sixty seconds so my game would contact the advert provider and request a new ad every minute. After a while I decided to make the adverts somewhat less intrusive by changing the refresh rate down to 120s, or once every two minutes. This is the maximum interval you can put into the Admob interface. This had the obvious effect of reducing the number of overall ad impressions by about half and roughly doubling the CTR and ecpm. The outcome being that revenue stayed roughly the same but the number of adverts I was showing was halved.
I kept the higher refresh rate as I decided that a good general principle would be that showing less adverts is less intrusive to the user. I don't know how true that is, after all is it better to show one bad advert for two minutes or a good and a bad one for one minute each? It probably doesn't make any difference either way and the net effect is the same. One thing I can say though is that less advert requests does mean less network traffic for the user and some mobile users have quite tight monthly data budgets.
Jump forward to the past two weeks and I released my new game "Super Snake Slot Machine". When publishing it I forgot to set the refresh rate in the Admob interface and it got left at a setting of "no refresh". What that meant was that an advert was requested when the game started but then no new ads were shown after that. The effect was that the CTR for Super Snake was about 5% compared to the 1% CTR I was regularly getting on Cherry Chaser at a 120 second refresh.
I had nothing to compare against so I set the refresh rate on Super Snake to 120 seconds for a couple of days and CTR plummeted back down below 1% whilst the number of impressions more than quadrupled. The overall revenue dropped slightly at a time when I would have expected it to be rising in line with the number of active installs. After setting the refresh rate back to "no refresh" the revenue rose again, although only in line with the growth of the user base.
I've now also set Cherry Chaser (which has 130,000 active installs compared to Super Snake's 4000) to also disable the refreshing of adverts. This has had no noticeable affect on overall revenue which has remained about the same. Number of ad impressions has dropped by a quarter and the CTR has risen by the same factor of four.
An unknown aspect for me here is how your CTR affects the quality of the adverts that are sent to your app. I've heard hints that a higher CTR will mean you are sent ads that give higher profits. It's very hard to tell if that is a real effect because you only have the one figure which could be affected either by the quality of the ad or the length of time it is displayed. I've read that CTR is a very important factor in Adwords ads with higher click words drawing a higher revenue. I don't see that the same principle will automatically apply in the mobile app advertising space though.
In conclusion it seems to be better to have higher CTR and a lower number of impressions by completely disabling advert refreshing. If nothing else it reduces the bandwidth usage of the app slightly. It may just be something about my own app that means this works and I can't rule out that a coincidental fluctuation in advertising rates has misled me to believe that the revenue is slightly better. I feel somewhat like I'm swimming against the tide of convention by disabling advert refreshes but so far nothing in the figures shows it to be a bad decision.