You probably have heard of A/B Testing where you have two versions of your page, serve them randomly to your visitors and track which works best. But there is a more advanced version of this, Multivariate Testing. This (obviously) involves multiple possible designs and of course it gets more complex to setup and analyze.
For #WordPress the Google Website Optimizer Plugin comes to the rescue to automate things, standing in the shoulders of course of Google's Website Optimizer service for the tracking and statistical analysis part.
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