A/B Testing SEO friendly

A/B Testing for SEO

I love testing. In my opinion, Website Testing is one of the most important conversion optimization techniques. However, it should be used taking into consideration the wider context of online marketing. In this post I will show a case study on how to account for SEO when doing A/B testing in websites. I will first discuss how A/B test can hurt SEO and then provide a way to solve the issues that might be caused by A/B tests.

Is My AB Test Hurting My SEO Efforts?

We used an A/B testing tool to conduct the experiment, and tested several homepage versions under the following URLs: example.com, example.com/index2.html, example.com/index3.html, etc. Two weeks after initializing the test, in a routine check of the website's indexed pages at Google, using a standard search query (site:www.example.com) we found, to our surprise, that the alternative homepage version had been indexed by Google.

This is so surprising because, theoretically, A/B tests redirect using JavaScript and they should keep the variations uncrawled and unindexed. This certainly holds true to multivariate tests, which do not redirect visitors from page to page, but show different versions inside the same page. But in this article we will show that it does not always hold true when it comes to A/B tests (read more about the differences between AB and Multivariate tests).

Website Tests Do Not Occur In a Void

To identify the source of crawlers into the alternative homepage, we checked for backward links to that page using the Google operator link (e.g. link:www.example.com/index2.html). There was a single external link pointing to that page. The link to the alternative URL appeared in an article quoting the website published in a business review website. We realized that the article's author, attempting to insert a link, entered the website's URL during the trial period and was served an alternative homepage version. He then copied the alternative URL and pasted it in his article. The crawlers' path to accessing and indexing the alternative homepage version was clear. Mystery solved!

There is an important lesson to be learned from this case: although A/B tests work under a controlled test environment, one that is also blocked from search engine crawlers, tests do not occur in a void. Test participants (i.e. site visitors) operate as the gate out of the closed test. Participants are unknowingly given test versions, which they can save as bookmarks, or add as a link in their blogs, unaware they are linking to a test version.

Accounting For SEO When AB Testing

Our solution involved two steps:

  1. We immediately added the alternative URL to the site's robots.txt file to disallow crawling. This method guaranteed that the alternative homepage version would not be indexed by search engines.
  2. After the A/B testing was complete, the chosen page version was set to the original homepage URL. We then added a permanent redirection (301) of the alternative URL (/index2.html) to the original homepage URL. This would channel any traffic attempting to enter the site via alternative link versions, correct the homepage, and avoid dead end traffic caused by broken links.

This example shows us that, once again, search marketing should be viewed as a conglomerate of variables, where SEO, paid campaigns and Web Analytics are intertwined. Each effort to optimize a website should strengthen all others to increase synergy and boost revenues.

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