A good article on Smashing Magazine about A/B testing and about how to use data to make decesion optimizing the website design. Ashley discussed different terms at first like:
Quantitative data: Numerical data that shows the who, what, when and where.
Qualitative data: Non-numerical data that demonstrates the why or how.
Empirical data: is any type of information gathered through observation or experimentation.
And then moved to an experiemnt with how they used the data from Google Analytic to target a specefic audience making a new landing page with a great results at the end, she also mentioned some great advices like tailioring the landing page to specefic audiences, set a business goal, define what sucess is for the team and also she mentioned some online tools in addion to Google Analytic like Optimizely.