4. What factors influence how often a given ad is served?

Google claims there are three main factors that influence how often a given ad is served, here’s what they say:

• Ad Rotation – By default, all campaigns are set to optimized ad serving. This means that if one ad has a higher clickthrough rate (CTR), it will show more frequently than the other ads in your ad group. This system automatically favors better-performing ads that drive more traffic to your site. You can opt out of optimized ad serving if you’d like the AdWords system to rotate your ads roughly evenly. If you do so, note that your ads still may accrue different ad served percentages or numbers of impressions. This is because the AdWords system considers an ad’s Quality Score when ranking it on a search result page. An ad with a high Quality Score may appear on the first page of search results, where it accrues an impression every time it’s served. On the other hand, an ad with a low Quality Score may appear on the second page of search results, where it will only accrue an impression if the user clicks through to that page.
• Time – If an ad is created late in the day, it will have a lower ad served percentage at the end of the day than the existing ads. This difference will decrease over time.
• Approval Status – If an ad has yet to be reviewed and approved, it’ll only appear on Google. If it isn’t yet generating impressions on the Google Network, an ad will have a lower ad served percentage. This means if you’ve been running an ad and then replace it with a new ad, you may see a drastic decrease in clicks and serve percentage for the first couple days while the new ad is being reviewed and approved.

5. What is Ad Rotation?

Ad rotation refers to the way your ads are delivered on Google and the Google Network. Your ads will rotate if you have multiple ads within an ad group, since no more than one ad from your account can show at a time. You can, however, specify how you’d like the ads in your ad group to be served. The first option for ad serving is Google’s default setting of Optimize. Optimized ad serving delivers ads with higher clickthrough rates (CTRs) into the ad auction more often than other ads in the ad group. These higher-quality ads gain more impressions than other ads in the ad group, resulting in higher ad served percentages. By using this ad serving option, your ad group will likely receive more impressions and clicks overall, since higher-quality ads attain better positions and attract more user attention. The second option is to have your ads served in a set rotation. Rotated ad serving delivers ads more evenly into the auction, even when one ad has a lower CTR than another. The impression statistics and ad served percentages of the ads in the ad group will be more similar to each other than if you had selected the optimization option. However, these statistics still may differ from each other, since ad position may vary based on Quality Score and CPC. The second post in this series will be published early next week, so stay tuned.

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