Prusak.com

When running an A/B experiment Google Website Optimizer appends any parameters from the original page when redirecting to one of the test pages.

For example, the original page is index.php and the test page is index2.php.
If a user clicks on index.php?name=fred they will be redirected to index2.php?name=fred

So what happens if the test page URL already has a query parameter in it?

For example, the original page is index.php and the test page URL is index2.php?section=b
What will happen if the user clicks on index.php?section=d ?

About seven months ago I had a client with this exact scenario so I tested it.
The user was directed from index.php?section=d to index2.php?section=b&section=d
I found a work-around and didn’t think about it after that.

A few weeks ago I found out that Google was indeed aware of this “issue” and fixed the GWO code 🙂
Now GWO will merge the parameters from the two URLs, not just append them. The parameters defined during setup for the test page URL will get precedence over the parameters from the URL the user clicked on.

For example, the original page is index.php and the test page URL is index2.php?section=b
What will now happen if the user clicks on index.php?section=d&cat=22 ?

They’ll be redirected to index.php?section=b&cat=22

This doesn’t effect 99.99% of all A/B tests, but if it does effect you, Google’s fix is a life saver 🙂