Are you testing new ad copy on Google? Are you trying to see if a new ppc advertising ad will outperform an old ad? One thing you should be aware of is that by default Google will optimize the serving of ads, meaning that over time it will show the best performing ads more often (based on click-thru rate). A vast majority of the time this is a good thing. You want the best performing ads to show more often because this will help keep your click-thru rate up, help keep your quality score strong, etc.
However, sometimes a newer ad never really gets a true chance to prove itself because a strong older ad quickly overtakes it. This leads the new ad to languish and die a quick death because the percentage of time this new ad is shown quickly plummets if it doesn’t immediately outperform the older ad. Of course, sometimes that is okay if the new ad really is that much worse than the older ad.
But what if you really want to test an older ad with a newer ad on a level playing field? Then what do you do? Google does offer the opportunity to rotate ads on a more even basis. If you navigate to the Edit Campaign Settings screen in your Google AdWords account, you will see a Scheduling and Serving category where you can choose to either Optimize the ad serving (the default setting) or you can choose to Rotate and show ads on a more even percentage basis. By choosing to rotate ads more evenly you will allow a newer ad to run 50/50 with an older ad. After a set period of times has elapsed, you can then compare the click-thru/conversion rate of the ads and see how well they have performed against one another. This isn’t necessarily something you want to do all the time, but it is certainly worth taking a closer look at once in awhile if you really want to test ad copy in a true head-to-head battle.