Abstract
Recent research has established the importance of defining usability requirements as part of the total requirements for a system. Instead of deciding in an ad hoc manner whether or not a human-computer interface is usable, measurable usability requirements are established at the outset. It is common to state such requirements in an operational manner: U% of a sample of the intended user population should accomplish T% of the benchmark tasks within M minutes and with no more than E errors. The formal experiments needed to test compliance with the requirements makes this method costly. This paper presents an alternative method of specifying usability requirements currently being developed and tested on a large software project at Virginia Tech.
Briefly, usability requirements are specified by having every member of the software design team and the user interface design team specify the ease of use desired for each proposed functional requirement of the system under development. The individual ratings are then compared in order to arrive at a consensus. It is this consensus that leads to the formal usability requirements which the interface must meet or exceed. As the interface is built, it is rated in the same manner as that used originally to specify the requirements.
This method thus provides a structured means of specifying measurable usability requirements and a means of determining whether or not the interface satisfies those requirements. Several other benefits of this method are presented as well.
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