I had a Problem that with the new Adsense Interface I could not figure out
how to get correct statistics about Placement targeted Ads on my Channels.
Displaying my Channels by "Targeting type" showed very low Page impressions
but a much higher Click count which I could not really explain.

So I asked on Google groups and was pointed to a very interesting answer
from Engineer Guillaume a Google Employee helping users on Google groups for Adsense


We are aware of this problem. In a nutshell, page views are counted only
for the first ad unit of the page.
It affects all publishers; it is not a temporary glitch but a question of design.

Unfortunately there seems to be no solution that shows correct CTR and RPM in the
ad units report while keeping reports consistent with each other. We would be happy
to get your input if you have ideas about how to improve the situation.

In the mean time, we recommend using 'page unit impressions | queries' column
instead of 'page views'. We are considering making it the default to reduce confusion.

If you are interested, below is a detailed explanation of the problem:

As you noticed, when there are multiple ad units on a page, only the first one gets
the page view. Each page view is counted exactly once in each report, so the total of
the 'page views' column is the sum of all 'page views' values in the report, and matches
the other reports. (Let's ignore the special case of custom channels.)

Reports where each page view has statistics for a single row in the report behave as
expected: Days/Weeks/Months, Products, URL channels, Sites. For instance,
a given page view / click belongs to a single day.

The problem is for reports where a single page view generates statistics for multiple rows:
Ad units, Ad sizes, Custom channels, Ad types, Targeting types, Bid types. For instance,
if a page contains ad units with different ad sizes / ad types / etc., then only the
ad size / ad type / etc. of the first ad unit will get the page view.
The other gets no page views, hence show invalid page views, page CTR, and page RPM.

If page views were counted for all ad units, not only the first one, then the total for
the 'page views' column on an ad unit report would be wrong and inconsistent between
reports. For instance, let's assume that we have 10 page views for a page
containing 3 ad units, all of the same size. The 'ad units' report would show
10 page views per ad unit = 30 page views total (wrong), hence an incorrect
total page CTR and page RPM. All ad units have the same size, so the 'ad sizes' report
should show 1 row with 10 page views, which would not match the 'ad units' report.
Showing 1 row with 30 page views would be wrong too,
because there were only 10 page views in reality.

As you can see, we are in a dead end: whatever we do, the 'page views'
total is wrong and/or inconsistent across reports.

A last remark: a similar issue affects ad unit impressions | queries for ad-level reports
such as Targeting types and Bid types. The individual ads in an ad unit can have
different targeting types or bid types. However, it is nearly invisible because:

  1. Targeting types and bid types are evenly distributed among the ads of a given ad unit, so the corresponding reports are statistically sound.
  2. No report allows getting statistics for the ads by position in their ad unit.

Link to the original thread:
Page views drop on 2nd units for several months : statistics totally wronged - AdSense Help

This was the reason for my stats problem too.
In case you have the same problem, in the upper right there is a "Column" drop down.
Select "Ad unit impressions | Queries" instead of page views and you get the number
of Ad Impressions which is what I was looking for.

Kind regards