Back in October I mentioned that Google had launched a beta program called Website Optimizer to make it easy to perform multi-variate testing on you your site. Website Optimizer is now open to everyone with an AdWords account.
For a quick refresher A/B testing allows you to make a change to a web page and compare the new version against the original to see which performs better. Multi-variate testing allows you to test several variations and combinations of changes against each other so you might test two versions of a heading with two versions of text on a call to action and compare every possible combination of headings and text to see which works best. You can think of it as A/B testing on steroids.
ClickZ has done a brief write up, Google Unwraps Multi-Variate Site Testing, Anoints Partners, along with news that Google will partner with some trusted consultants to help users set up and analyze tests. And you can get an overview of Website Optimizer from AdWords Help Center.
If you currently use AdWords then signing up for Website Optimizer should be a no-brainer.
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