Information Technology Reference
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Severity ratings help focus attention on the issues that really matter. There's
nothing more frustrating for a developer or business analyst than being handed
alistof82usabilityissuesthatallneedtobefixedimmediately.Byprioritizing
usability issues, you're much more likely to have a positive impact on the design,
not to mention lessening the likelihood of making enemies with the rest of the
design and development team.
The severity of usability issues can be classified in many ways, but most sever-
ity rating systems can be boiled down to two different types. In one type of rat-
ing system, severity is based purely on the impact on the user experience: The
worse the user experience, the higher the severity rating. A second type of sever-
ity rating system tries to bring in multiple dimensions or factors, such as busi-
ness goals and technical implementation costs.
5.3.1 Severity Ratings Based on the User Experience
Many severity ratings are based solely on the impact on the user experience.
These rating systems are easy to implement and provide very useful information.
Theyusuallyhavethreelevels—oftensomethinglikelow,medium,andhigh
severity.Occasionallythereisa“catastrophe”level,whichisessentiallyashow-
stopper(delayingproductlaunchorrelease—Nielsen,1993).
When choosing a severity rating system, it's important to look at your orga-
nization and the product you are evaluating. Often, a three-level system works
well in many situations:
Low: Any issue that annoys or frustrates participants but does not play a role
in task failure. These are the types of issues that may lead someone off course,
but he still recovers and completes the task. This issue may only reduce effi-
ciencyand/orsatisfactionasmallamount,ifany.
Medium: Any issue that contributes to significant task difficulty but does not
causetaskfailure.Participantsoftendevelopworkaroundstogettowhatthey
need. These issues have an impact on effectiveness and most likely efficiency
and satisfaction.
High: Anyissuethatleadsdirectlytotaskfailure.Basically,thereisnowayto
encounter this issue and still complete the task. This type of issue has a sig-
nificant impact on effectiveness, efficiency, and satisfaction.
Notethatthisschemeisaratingoftaskfailure,oneofthemeasuresofuser
experience. In a test in which there are no task failures, there can be no high
severity issues.
Another limitation of a three-level scheme from low to high is that user expe-
rienceprofessionalsoftenarereluctanttousethe“low”category,fearingthat
those issues may be ignored. That limits the scale to two levels.
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