AdSense Experiment: The Final Summary

As you may remember, I’ve been running a little AdSense experiment on this site. Here’s a brief summary for new readers:

The core motivation for the experiment was to test the prevalent assumption that people coming from search engines are the ones most likely to click on ads. To this end, I used a little piece of JS that would present different ads to people based on how they arrived on this site – either directly, from a search engine, from another kind of external site, or from a different page on the same site. All the ads were visually identical but were tracked separately.

(See the original announcement and the first summary for more details.)

The visitor segmentation script has been running uninterrupted for more than five months, allowing me to collect CTR and CPM data on more than 10 000 AdSense clicks. Overall, the trends look stable enough that running it for a while longer probably wouldn’t change the results. So now is a good time to post one final summary and declare the experiment concluded.

Internal Traffic Wins

At least on paper, it does. Out of all possible traffic sources, internal traffic – i.e. people who browse more than one page into the site – has the highest click-through rate and the highest eCPM. However, it also accounts for the least number of ad impressions. In a nutshell, internal traffic is valuable but rare.

Conversely, search engine traffic comes third in terms of CTR and eCPM, but brings the most money due to a high number of impressions.

The full results are below. To comply with AdSense ToS which prevent me from displaying the actual numbers, the results have been normalized to display the relative CTR and eCPM of various traffic sources.

Source Data

The above results are based on:

  • > 18 000 clicks.
  • > 400 000 impressions (73% search engine traffic).

All data was collected during an uninterrupted 168 day period (2010.03.09 – 2010.08.24) on this very same site. Results may be different for other sites.

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4 Responses to “AdSense Experiment: The Final Summary”

  1. So, given what you’ve learned, what impact will this have on your AdSense setup?

    Also, for reference, might you share the part of the TOS that prohibits sharing your actual figures?

  2. (ah, found it)

    Confidentiality. You agree not to disclose Google Confidential Information without Google’s prior written consent. “Google Confidential Information” includes without limitation: … (b) click-through rates or other statistics relating to Property performance in the Program provided to You by Google…

  3. White Shadow says:

    The only immediately actionable result is that, assuming average CTR matters, I could stop showing ads to direct visitors.

    The real value of collecting this sort of data is that now I can build a statistical model of impressions/CTR vs earnings and feed in various “what if” scenarios to see what kind of on-site/off-site optimizations would be most profitable.

    For example, I have an Excel spreadsheet that lets me quickly get answers to questions like “Which is more profitable – increasing the search traffic by 10%, or increasing the number of visitors who click through to another page on the same site by 10%?” This helps with decision making.

  4. After reading a piece on this very same type of study I too crunched the numbers and made some decision about who sees adverts. Removing advert exposures for groups of people who weren’t clicking on them anyway was part of this. Another was the aesthetics of the layout, and rewarding repeat or non-search engine visitors to my travelogue by hiding various AdSense/sidebar components.

    FYI – AdSense can go a long way to helping give you some rough ideas about who is clicking on what based on the type:

    I found this helpful:

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