If you were publishing a newspaper, you wouldn't care who read it. As long as the number of readers was nice and high, it wouldn't matter too much to you whether they all read one article or absorbed everything from cover to cover.
That would be true even if you were publishing a free newspaper.
You'd just want know how many people your publication reaches so that you can charge advertisers the right price.
Online, things are a little different. Although you do want your traffic levels to be as high as possible, not all users are worth the same to you or to your advertisers.
It all comes down to your traffic sources. If you have a link on a site that's not closely connected with the topic of your blog -- or one whose users tend not to click ads -- you might generate lots of impressions but very few clickthroughs.
No tinkering with placement or formats is going to change that. Some users just don't click ads.
Digg.com, for example, is famous among publishers for shooting up page views but having little effect on ad clicks.
One way to get around that problem is to also put CPM ads on your site. Because they pay per every thousand impressions, even if a site is bringing you traffic with a very low clickthrough rate, you'll still earn something from them.
But even that might not be a solution. Advertisers can see where the impressions were made and often pay lower rates for people outside the United States. Users located in some countries are even worth nothing to them at all and they won't count towards your total ad impressions.
That's why when you're looking at your impressions and your clickthrough rate it's important to consider not just your traffic levels and your AdSense optimization, but also the quality of your traffic. Sometimes, you can improve your revenues more with better traffic targeting than you can by repositioning your ads.
It's Del.icio.us!
Furl It!
