Split testing works. Use it well, and you will improve your conversion rates, and, thus, your profits. And, if you are advertising, or have significant product costs, raising your conversion rate just a little can raise your profits a lot. But there are many different kinds of split testing software out there.

Let me give you an overview, so you can understand the choices you have before you. I’ll walk you through the main distinctions that rule the field.

First, there’s a difference between multivariate and single variable 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.

Google offers a single variable split testing tool, but you have to have an Adwords account to use it.

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.

There are further distinctions among multivariate split testing tools. There are hosted solutions, and solutions you install on your server. Typically a split testing program can run a little more quickly if it’s on the same server as your webpage. Installed programs tend to be less expensive, too. You also will have complete control of your data. On the other hand, with a hosted solution, you don’t have to do an installation.

Google Website Optimizer is a hosted plan. But it requires you to have an Adwords account and an analytics account. There is also a reporting delay. Other hosted plans include SiteSpect, and Offermatica. The Split Test Accelerator an MuVar are installed solutions.

Another 3-way distinction among multivariate split testing tools is between Taguchi-based systems, Full factorial systems, and Random independent rotation of factors. With a Taguchi system, you run traffic to only a small, carefully-selected subset of the possible combinations of your factor levels. This allows you to cycle through every combination every 12, 18, or 36 pages, whichever the case may be for the test design you’re using. This allows you to find the best combination very quickly. Some care does have to be taken to avoid interaction effects among the factors. Taguchi-based tools include the Split Test Accelerator and Vertster.

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.

Some multivariate tools randomly serve the options for each factor independently from what is served for the other factors. This can lead to more flexible test design, but also to more interaction effects and other statistical noise, leading to longer 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.