Jakob Nielsen might be the guru of web usability, but his recent AlertBox has troubles with numbers. In his most recent Alertbox, How Big is the Difference Between Websites (http://www.useit.com/alertbox/20040119.html), he tells us that the average difference in usability between websites within the same industry is 68%, based on the time it takes to do a variety of operations. Then he goes on to say,
Half the time, of course, you'll get the sad message that you're 68% worse than your competitor. This verdict has one redeeming quality: it's very motivating data to show to your upper management. After seeing it, they're much more likely to support a major change in your Web design's direction, with more emphasis on usability and customer service.
Yes, he admits that the actual scores vary widely, but it is rather unlikely that you will score 68% above or below your competition.
What I would rather know is how big a difference is "big." For instance if the difference is 10%, is that important? Web usability is a interesting world because the standards keep raising as designers learn new approaches and as users become familiar with those approaches, and Nielsen discusses this. Website design is an area where continuous improvement is the mantra, so at least designers are familiar with the issues Nielsen presents, even if his discussion of the numbers is a little off.