I read once about a man who tripled his conversion rate by changing a single letter in his headline. While that kind of improvement is not common (not by a long stretch), you can quite probably double your conversion rate after testing 10 or 20 items on your page. With that said, there are many things to consider when getting started with split testing.

I can’t discuss every feature of every testing tool out there, but I can give you a major overview of the different kinds of split testing software.

The first main division is between simple split testing (single variable) and multivariate testing.

Simple split testing is easy. You’re just “trying stuff” one thing at a time. You want to try a different headline? Split test it. When that test finishes, you want to “try” something else? Split test that. You can test one alternative version or many. As long as it’s a single element of your page you’re testing, that’s simple split testing. All you need is a tool that rotates the different versions of the headline (or whatever) on your page, and keeps track of which one produces the most sales.

Paul Hancox has a simple split testing tool. And Google has one that’s free, though it takes a bit to set up all your accounts to use Google’s tool. And the reporting is not real-time.

Single variable testing can be slow. How would you like to test 10 times as much with the same amount of traffic? Well, you can. You use a method called multi-variable, or multivariate testing. This allows you to test several elemens on your page simultaneously.

Among multiple variable software solutions, there are hosted plans and self-install plans. If you want to install software on your server (which can be faster and cheaper) you will have more control over your data. And you can usually find someone to install it for you (often the vendor provides this service for a nominal fee). If you want to go with a hosted plan expect to pay more.

Hosted solutions include Google’s Website Optimizer, and Vertster. Installed solutions include the Split Test Accelerator and Kaizen Track.

Taguchi testing is only one kind of multivariate testing. There are also “full factorial” tools, and random independent rotators. When you run a Taguchi test, you run only a small fraction of the possible combinations of your factor levels. You might, for instance, run only 18 pages to test 4374 combinations. This is made possible by orthongonal arrays. This allows you to find the best combination with out running through all of them. You do have to be careful about your factors interacting negatively with each other, but if you take care as you design your test, you can avoid the bulk of the problem with these. The Split Test Accelerator, Vertster, and Kaizentrack are Taguchi testing tools.

If you want to get around interaction effects you can with a full factorial tool. It will take more traffic to avoid the interactions — a lot more — but with a FFT, like Google’s Website Optimizer, you can just see how every combination plays out, and live with the interactions.

The Taguchi and full factorial tools both use arrays to maintain a relationship between the options being served for one factor, and the options being served for another. Some split testers don’t do this, though. They simply treat each factor as independent from the other factors. This leads to more flexible test designs, but also to longer and less accurate tests.

Now that’s just the overview. There are many other features to compare and questions to ask. Does a tester allow you to exclude bots and spiders? Does it allow real time access to data? What kind of reports does it show? What kind of information does it track for each visitor, and is the visitor-level data available for viewing. Etc.

Dominic DeLong has used multivariate testing tools for years to improve landing pages.