Over the past several years, I’ve grown increasingly dissatisfied with the vague and somewhat solipsistic nature of the gradations UX professionals typically use to describe the severity of usability issues. High, medium, and low don’t begin to sufficiently explain the potential brand and business impacts usability issues can have. After incrementally iterating on several existing classifications of severity, I finally decided in late 2008 to simply create some new ones, which I’ll present in this column. For lack of a better term, I call them business-aligned usability ratings.
Despite usability questionnaires providing only a partial picture of usability, they are nonetheless important. In fact, you could argue a user's perception of an application's usability is more important than actual task performance—a sort of gateway measure of usability.
Consider what is the most critical action you want your customers to accomplish on your site—what is your primary conversion? For an ecommerce site, the purchase that a thank-you confirmation represents is commonly the key conversion. From there, work backward to determine the key steps a user takes to get to that conversion point.