Information Technology Reference
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specific action or set of actions that may result in task failure. For example, a user
may make the wrong selection on a web page and sell a stock instead of buying
more. A user may push the wrong button on a medical device and deliver the wrong
medication to a patient. In both cases, it's important to know what errors were made
and how different design elements may increase or decrease the frequency of errors.
Errors are a useful way of evaluating user performance. While being able to
complete a task successfully within a reasonable amount of time is important,
the number of errors made during the interaction is also very revealing. Errors
can tell you how many mistakes were made, where they were made while inter-
acting with the product, how various designs produce different frequencies and
types of errors, and generally how usable something really is.
Measuring errors is not right for every situation. We've found that there are
three general situations where measuring errors might be useful:
1.
When an error will result in a significant loss in efficiency—for example,
when an error results in a loss of data, requires the user to reenter infor-
mation, or slows the user significantly in completing a task.
2.
When an error will result in significant costs to your organization or the
end user—for example, if an error will result in increased call volumes
to customer support or in increased product returns.
3.
When an error will result in task failure—for example, if an error will
cause a patient to receive the wrong medication, a voter to vote for the
wrong candidate accidentally, or a web user to buy the wrong product.
4.3.2 What Constitutes an Error?
Surprisingly, there is no widely accepted definition of what constitutes an error.
Obviously, it's some type of incorrect action on the part of the user. Generally an
error is an action that causes the user to stray from the path to successful com-
pletion. Sometimes failing to take an action can be an error. Errors can be based
on many different types of actions by the user, such as the following:
•
Enteringincorrectdataintoaformfield(suchastypingthewrongpass-
word during a login attempt)
•
Makingthewrongchoiceinamenuordrop-downlist(suchasselecting
“Delete” instead of “Modify”)
•
Takinganincorrectsequenceofactions(suchasreformattingtheirhome
media server when all they were trying to do was play a recorded TV
show)
•
Failingtotakeakeyaction(suchasclickingonakeylinkonawebpage)
Obviously, the range of possible actions will depend on the product you are
studying (website, cell phone, DVD player, etc.). When you're trying to deter-
mine what constitutes an error, first make a list of all the possible actions a user
can take on your product. Some of those actions are errors. Once you have a uni-
verse of possible actions, you can then start to define many of the different types
of errors that can be made using the product.
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