If you are using the build in AdSense Feature of DFP like I described here: How to set up Google AdSense using DFP Small Business build in AdSense option then you need to create a new Order, a Line Item and setup AdSense as Creatives if you want to be able to run a split test.
Read my old approach on how to display AdSense with DFP Small Business here: How to set up Google AdSense as Line Item using DFP Small Business
With DFP you can easily run tests like a 50:50 Split test to see which Ad performs best for your website. I for one did several split test just this week.
I ran Large Rectangles inside my first posts of each thread of my forums and I wanted to see if a medium rectangle performs better.
I first created a new AdSense Channel for the medium rectangle to track the results and a medium rectangle AdSense Ad Unit to which I assigned the newly created AdSense Channel.
Then I created a second creative for my medium rectangle inside the Line Item which serves the Ads inside my first posts. So now this Line Item contains 2 creatives, one for my large rectangle and one for my medium rectangle.
Both creatives are served evenly (Line Item Setting: Rotate creatives > Evenly) which means in a 50:50 manner.
Now you let both Ads run for let’s say 30days and then compare their performance in your AdSense Reports interface by comparing both channels of the Ads.
If you see that one Ad Unit outperforms the other Ad Unit simply disable displaying the corresponding creative in DFP and you just increased your income for that Ad Spot.
Do this with all changes and over time you will optimize your Ad Inventory to maximize your revenue.
My recent split tests:
I serve a medium rectangle inside the first post of each thread on my medical forum.
Currently the Ad is set to serve Image&Text Ads.
In general the more competition there is for an ad unit the higher your CPC will be. However not always does a higher CPC results in higher earnings!
For about 2 years now I never thought it might be possible that images or text only ads would earn me more then image&text.
But like I said, I do like testing and so I started testing.
I took one of my sub forums as testing ground and run the test for 2 weeks.
Example from my recent split tests (no real values due to AdSense ToS but these reflect my results):
Each Ad Unit got around 40k Impressions
Image & Text: CTR ~0,9 | CPC ~34 Cent | RPM ~2,9 Euro
Text only: CTR ~0,3 | CPC ~17 Cent | RPM ~0,44 Euro
Image only: CTR ~1,0 | CPC ~31 Cent | RPM ~3,2 Euro
What does this tell me? (not you! You need to test for yourself to see impact for you)
a) Never ever serve text only ads
b) If I switch to Image only Ads I earn 30 Cents more per 1000 Impressions
c) Even though that the CPC for ‘Image only’ is lower then ‘Image & Text’ Ads, my visitors seem to click Image Ads more often which results in a higher RPM
d) I will expand the test to see if this is a phenomenon in my sub forum or if it works the same way for different topics
e) I made a note to myself to run this test again in about 6-8 month after I switched to image only Ads
With investing 5 minutes to set up the split test (and of course running it for 2 weeks+) I increased my monthly earnings.
Will this work on all my forums? Probably not.
Will these conclusions be valid forever? Definitely not!