Thanks Gerardas,
This site was actually the inspiration for my swing at this type of application. I heard about it on a Perry Marshall call and tried it out on a few campaigns I was running. Although it seemed to work, it didn't mention anywhere about how the significance was derived. I asked my wife about it and she pointed me to the chi squared statistics test commonly used in clinical trials.
I setup the chi squared formula in Excel, but couldn't replicate the results achieved at splittester.com. To ensure I had built the formula correctly, I located a few chi squared calculators at some university websites - everything checked out. I then just transferred my excel worksheet to PHP code and ran the same tests.
While I'm not saying the results at splittester.com are incorrect, I was just uncomfortable with the lack of detail on how the results were derived.
Truth be told, I was learning PHP at the time and was really just looking for an excuse to do a little coding in it.