I just noticed on the AdSense What is New Page for August that in addition to the new way of setting up search to show on your own domain that they’ve added an extra option for viewing stats in advance reports.
Now instead of just viewing impressions either by ‘ad unit’ or ‘page’ publishers now have the option of viewing their stats by ‘individual ad’.
You see the options in the ‘Show Data by’ drop down menu.
The new option allows you to see your stats (CTR, eCPM etc) for each individual ad shown on your site. So on a skyscraper ad unit where 4 individual ads might be served to your blog this counts as 4 individual ad impressions. Alternatively if you view by ‘ad unit’ it would count as 1 impression and if you were to view by ‘page’ even if you had multiple ad units on the page it would only be counted once.
Google explains it elsewhere by explaining each of the three options like this:
• Page reports will show an impression every time a user views a page displaying Google ads. We will only report one page impression no matter how many Google ads are displayed on a page. For example, if a page with one half banner and one vertical banner is viewed once, we will display one page impression.
• Ad unit reports will show an impression every time a user views a Google ad unit on your page. For example, if a page with one half banner and one vertical banner is viewed once, we will display two ad unit impressions.
• Individual ad reports will show an impression for each individual ad that is shown in any ad unit. For example, if a page with one half banner and one vertical banner is viewed once, it will generate three ad impressions.
I generally look at my stats in ‘Page’ mode and rarely switch out of it. I guess it’s personal preference really as I know of other publishers who’ve preferred ‘Ad Unit’ stats.