Which ads have higher eCPM in Adsense – Text ads or Image ads ?

This post answers the following questions –
Which Ad type in adsense is good in ecpm ?
Which Ad type in Adsense is good in ctr ?

When I joined the program I was of the opinion that the Text ads get better earnings than the image ads. The main reason of my opinion was that text ads were attracting more clicks from the user. Image ads had lower Click Through Rates (CTR), so after a bit of experimenting I settled down for Text Only Ads.

At a later point, I read through Adsense optimization tips which suggested that a mix of Image and Text was the best solution. Though I was not very sure I still went ahead and changed the ads setting for one of my major site and the CTR went down by eCPM went up. Basically the Clicks went down but the effective Money we make for same page views increased. Let me explain with an example

Say if I have 1000 page views and my clicks are 70 and my earning is $ 3.0 with Text only ads.
Page Views – 1000
Clicks – 70
CTR – 7%
eCPM – $ 3.0

After I changed to a mix of Text and Image the equation changed

Page Views – 1000
Clicks – 50
CTR – 5%
eCPM – $ 3.5

Basically the image ads have more CPC, cost per click say than the Text ads, this could be because typically image ads take space of four different Text links and hence the higher CPC. Also google Adsense Blog says that Google tries to give either Image or Text based on whichever is more profitable to publisher.

So you can also do a bit of experiment and adjust your ads, according to the following is the order of performance

Text and Image Ads – Best
Text Only Ads – Good
Image Only Ads – Bad (many ads wont have image version and u will end up showing blank spaces instead of ads)