Reading the Stats For Link Units

Many publishers used to create a specialized channel to track the results of
their link units.
That’s still a good idea. But because link units require two clicks — one on
the unit and one on the ads the unit brings up — when you look at the
reports for link units separately, you’ll see a bunch of different data.
“Link unit impressions” shows the number of times users see a link unit.
“Link clicks” shows the number of clicks the unit receives. That figure will be
the same as the number of impressions for the ads themselves as each click
on a link unit pulls up an ad page.

“Ad clicks” describes the number of clicks received by the ads.
“Ad CTR” is the clickthrough rate of the ad page. It’s measured by dividing
the ad clicks by the link clicks.
Link CTR is the clickthrough rate of the link unit, measured by dividing link
clicks by impressions.
And Link eCPM is measured by dividing earnings by link unit impressions and
multiplying by 1,000 to show how much those units earn for every thousand
views.
If all of that sounds a little confusing, it’s a lot more accurate than looking at
link units together with standard units. When you look at your stats that way,
“clicks” refer only to clicks made on ads. “Impressions” however, include
both the link unit and the ads that appear on the ad page.
What you find when you look at the stats for your link units can be pretty
interesting.
It’s always been believed the CTR of the ad page is much, much higher than
the CTR of the link units themselves. Now we can see that’s true. What we
can’t do though is take action to improve the ad page CTR. We can’t change
the layout of the ad page or optimize it in any way to make it more attractive
to users. We can only change the design of the link unit itself.
That means that only one factor will determine whether lots of people click
the ads, or whether they click away.
The ads themselves.
You can’t choose the ads either but what you can do is create channels for
different link units on different keyword-optimized Web pages. You’ll then be
able to see which keywords have the best ads and the highest clickthrough
rates.
Most importantly, you’ll be able to see whether it’s worth replacing those link
units with other ad units, or targeting different keywords on the page using
AdSense’s Section Targeting.