Usability Problem Severity Ratings

Usability problems are typically rated as Severe, Moderate, or Minor.

Severe usability problems are those that prevent the user from completing a task or result in catastrophic loss of data or time. Catastrophic loss of data implies either that the lost data cannot be reconstructed or that there is a very high cost to reconstruction. Catastrophic loss of time must be considered in light of the task duration.
Moderate usability problems are those that significantly hinder task completion but for which the user can find a work-around.
Minor usability problems are those that are irritating to the user but do not significantly hinder task completion.

The standard of practice is that severe usability errors should prevent release of a product until those errors are eliminated or mitigated. At the very least, severe usability problems should not be tolerated in critical or frequently performed tasks.

Every effort should be made to fix or at least mitigate moderate usability problems before release of a product. Under no circumstances should moderate problems persist into a subsequent release.

If possible, fix minor usability problems prior to release. If that is not possible, the fix should be included in an item in the next release cycle though the item may be given a low priority of completion. The item should, however, be carried until it is addressed.

Example: A Severe Usability Problem

Situation: an illustration application has a File menu that contains Save and Revert menu items adjacent to each other. Neither menu item provides an informational message when selected—that is, when these menu items are selected the corresponding action is immediately performed.

Problem: the user sometimes makes selection errors by slipping on to the adjacent menu item. Either way this results in irrecoverable loss of data.

Solution: consider moving the items further apart, separating them by separator lines, and providing an informational message for the Revert menu item—but not the Save menu item because of the frequency with which this item is used. Whatever solution is chosen, this design flaw must be addressed because of the severity of its effect.

Last Modified January 2003. Send your comments?