Old websites get redesigned. Yahoo, for example, has seen over 10 redesigns since its launch in 1994.

My general attitude is that redesigns should be gradual rather than radical. User confusion is minimized while file integrity remains (massive changes can cause issues with your search engine indexing; even SEO-positive changes can hurt your organic traffic for months.)

Here is an example of a site taking a pretty major change recently, problogger.net. I am not going to criticize the redesign because I simply have no data to pass worthwhile judgments.

Original design:

New design:

So what steps should you take when redesigning your website? Is it important to hire a top web 2.0 designer? Or should your designer be sharp and clean?

Design is treated as an art. However, its impacts can be measured and manipulated as a science.

Google provides a very powerful free tool — Google Website Optimizer, (Adwords account required.) The name is generic but it functions as a multivariate tester. Traditionally, web publishers & marketers take two or more designs and run a split test to discover which more successfully accomplishes their goals. With multivariate testing you can run small tests of independent website elements and these determine which combination accomplishes your goals the most successfully (goals such as: ad clicks, e-mail sign ups, RSS subscriptions, product purchases, etc.)

(in this example, combination 4 received a conversion ratio of 1:3.5 while the original design converted at 1:7.3)

This is why I am in favor of evolutionary design — assuming your current design works. Just like with the scientific method, your need a controlled environment. When making major changes all at once, you lose that control.

When working in highly competitive marketplaces with a steep cost of visitor acquisition, an optimized design can be the difference between making millions of dollars or losing them. Of course, it doesn’t get any easier from here. Each individual visitor is unique. Geography, demographics, and even the time and day of the week are all variables in web site performance.

There is one dummy rule to use if you don’t care about this stuff (most people don’t need to) — keep it simple. Even your smartest users don’t want to learn a new user interface at every website they visit. Aim for the lowest common denominator and everyone will be happy.