Dave, as per your suggestion and encouragement, I have taken the plunge and signed up for Google AdSense. Now I've added it to my site and am getting some traffic and an occasional clickthrough. But I really don't understand the nuances between all the data shown in the report; can you walk me through the overview report in AdSense?

When I first signed up for AdSense I also found the reports pretty hard to figure out, I admit, but talking with a lot of folk, including AdSense guru Joel Comm (who sells a slick ebook called Google AdSense Secrets that's well worth the investment if you're serious about reinventing your Web site for better AdSense revenue) I think I've started to figure things out.

To be able to write this particular answer, I checked in with my colleagues at Google (it's helpful to have written a popular book about Google, I must say) and received permission to publish my actual AdSense reports here on the blog. So let's start there:

This is a snapshot from a few days ago at <ahem> some point in the day (while I have permission to share my actual earnings, it doesn't mean that I want to :-) so it gives you a sense of my overall traffic levels, percentage of ad blocks that receive clicks, and overall earnings: at this point in the day I'd already earned just a smidgen over $100.

Let's go down the left side first. Notice that Google splits out revenue by category, so here I have AdSense for Content (which includes this very content page that you're reading that has an AdSense block included), AdSense for Search (which is when I host Google searches on my site and then share in the PPC revenue if anyone clicks on an ad in the search result page), and Referrals (get someone else to sign up for AdSense or download the Firefox web browser with Google's toolbar already included and you can earn a small bonus).

I've talked about this before, but again notice how for me, as for most people I know in the AdSense program, my revenue comes exclusively from AdSense for Content. Referrals are a bit more subtle, I admit, because people need to both sign up and earn a certain threshold amount before I'll get paid, so the sign-ups I get will hopefully pay out down the road.

Also, if there's one thing that you need to be conversant in as an AdSense for Content participant, it's channels. Channels let you differentiate between your Google ads on different areas of your site or, if you've more than one site like I do, between sites. The figure shown is aggregated across all sites that I have in the AdSense program, so if I burrowed in further you could see that some sites have much lower traffic but superb per-click earnings, while others have huge traffic and almost no clicks at all. But channels are a different posting, so let's stay focused on this report.

Now, across the top on AdSense for Content: page impressions are essentially the number of Google AdSense blocks that I've displayed on my Web sites. Since I can have more than one block on a page (you can have up to three) this isn't the same as number of page views or number of visitors. Indeed, this page you're looking at has three ad blocks, so your viewing will count for three, not one, page impression. Also note that PSAs (public service ads) for non-profits don't count as page impressions, so if you see lots of PSAs on a site, it'll be skewing this number relative to site traffic.

The next value is clicks, and that should be fairly obvious: someone clicks on an advert and this value increases. Divide page impressions by clicks and you should end up with Page CTR, page click-thru rate. My rate here is 2.7%, which isn't too shabby. It means that for every 1000 ads I show, 27 will be clicked upon and a visitor paired up with an advertiser. This is an important figure because if you can increase your CTR, you can generate more revenue without having to drive more traffic to your site.

The next field, the one that's probably the most puzzling, is the Page eCPM, which is (ready for this?) the cost per thousand (M = mill = thousand in Latin. Those wacky advertising folk are to be thanked for this bit of confusion) or CPM equivalent rate for your ads. This is only important if you're clued into the advertising world: when advertisers buy a banner ad on a site, they pay based on the number of eyeballs, the number of people who see the ad. That is the "cost per thousand". So here Google's just taken the page impressions and divided it by earnings to produce what they call an "effective CPM" rate. This shows that if I were to charge $5.20 CPM for ads on my site, I'd exactly match this income level.

Again, for the majority of people, eCPM is not an interesting figure and can be safely ignored. Generally, a high eCPM means that your ads are more valuable than a low eCPM, but more than that's probably risky to conclude.

Finally, the value that people are usually most excited about: Earnings. That's the proverbial bottom line here, and I admit it, when I log in to my AdSense account I promptly check my earnings then back up to see the other figures.

There's a lot more data you can glean from the AdSense reports area, including seeing a report by day of all these figures, a report by channel across an arbitrary time period (answering questions like "which of my Web sites generated the most revenue last week?"), and even a combination of these reports. Start by clicking on Advanced Reports - Ad Performance to learn more.

I hope this rather exhaustive answer helps clarify exactly how to understand your Google AdSense report. If you haven't yet signed up for AdSense but are interested in learning more about how to monetize your existing Web site traffic, please do check out my earlier article on Getting started with Google AdSense.

Oh, and one final tip: don't click on your own ads! You might think it'll make you a few bucks, but since it can also get you kicked out of the program entirely, it's really not worth the risk!