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Brad Geddes's Theories on Marketing How Ad Rotation Affects Your AdWords Ad Testing

How Ad Rotation Affects Your AdWords Ad Testing

This post originally appeared on the adAlysis ad testing blog.

If you have multiple ads in an ad group; your ad rotation settings will determine how often each ad is displayed. Based upon how you are testing and your favorite metrics, you should consider the rotation setting you are using and how that affects your ability to receive statistical significance data to make testing decisions.

The Ad Rotation Settings

There are four ad rotation settings:

  • Optimize for clicks: the ad with the highest CTR should be displayed the most often
  • Optimize for conversions: the ad with the highest conversion rate should be displayed the most often
  • Rotate evenly, then optimize: the ads should have roughly equal impressions for 90 days, then the highest CTR ad will be displayed the most often
  • Rotate indefinitely: the ads should have roughly equal impressions



Ad Served Percentage

The ad served percentage shows you how often each ad was served across your account, campaign, or ad group.


When examining this data; it is important to keep in mind the time frame you are examining. If you have paused or deleted ads that were active during the timeframe you are examining, then your ad served percentages may not add up to 100% unless you show those ads.

In addition, it is useful to only examine the data when all the ads were running at the same time. If you create an ad one month ago; but you are looking at the last three months of data; of course it will look like the newer ad doesn’t have the appropriate ad served percentage; and it can’t as it wasn’t active for two of the three months you are examining.

Improper Ad Rotation

When you use any ad rotation setting except for ‘Rotate….’ (such as ‘Optimize for CTR’ or ‘Optimize for conversions’), sometimes AdWords makes decisions too quickly about which ad is likely to be a winner.

For instance, if the campaign had the ad rotation setting set to ‘Optimize for conversions’ and we examine a time frame where all the ads were active, we would expect to see that the highest ad percentage served would be the ad with the highest conversion rate.



Unfortunately, that is not always true. Sometimes AdWords makes decisions too quickly and the wrong ad has the highest ad served percentage. For example, the below campaign was set to ‘Optimize for conversions’. Ad two is the highest converting ad and has the highest click through rate; so by any ad rotation standards the second ad should have the highest percentage served. However, it does not.



This does not happen all the time by any means; however, it does happen. When your ads are served improperly, it affects your account’s goals and your ability to reach the minimum viable data in determining the true statistically significant winners.


How Ad Rotation Affects Minimum Viable Data

Any ad test should have a minimum amount of viable data, such as a minimum amount of time, clicks, impressions, and conversions. These may vary depending on the type of metrics you are using for ad testing and the type of keywords you are testing (such as brand vs product).


When your ad served percentages are skewed towards a single ad, then the other ads receive less impressions. Since they have less impressions, these other ads also receive less clicks and conversions. Since these ads are receiving less data, it takes longer for those ads to build up enough minimum viable data to make statistically significant decisions.

Use Rotate Indefinitely for Ad Testing

For most serious ad testers, you should be using ‘Rotate indefinitely’ as your ad rotation setting. This will ensure that your ads are equally served and that all the ads build up the minimum viable information to make ad testing decisions.

Even if you only care about conversion rate (and if you are in lead generation; there are probably better lead gen ad testing metrics) and think that using ‘Optimize for conversions’ is the best option; that is only true if you meet two conditions:

  • AdWords actually serves your highest conversion rate ad the most
  • You are removing losers as you have the data

This second point is an important one; take the metrics from this ad group that was not well looked after.


Ad % Served Conversion Rate Conversions
1 56% 9.0% 504
2 14% 8.3% 116
3 10% 7.2% 72
4 8% 6.1% 49
5 6% 3.2% 20
6 5% 1.1% 6
7 1% 0.9% 1
Total 100% 768


If ad 1 (with the highest conversion rate) had been served 100% of the time; then the ad group would have had 900 conversions instead of 768. As you should always be ad testing; there will be some opportunity cost when you test an ad that turns out to be a loser.

However, unless you are willing to test ads, you’ll never get better. Moreover, if your competition is diligent about testing, you’ll get worse by clinging to your old ads as they start to beat you.


To be a good ad tester, you should use ‘Rotate indefinitely’ as your ad rotation setting to ensure that all your ads are equally served. Then you need to be diligent about removing losers and creating more ads.

While this can be a lot of manual work, with good ad testing software, it can be very easy to find winner and losers and continuously test your ads so that your account keeps getting better and beats your competition.

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