User Interface Design and Ergonomics - National Open University of ...
User Interface Design and Ergonomics - National Open University of ...
User Interface Design and Ergonomics - National Open University of ...
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3.2 USABILITY CONCEPTS AND GUIDELINES<br />
The major concepts <strong>of</strong> usability are:-<br />
Efficiency: Once users have learned the design, how quickly can they perform tasks?<br />
Learnability: How easy is it for users to accomplish basic tasks the first time they<br />
encounter the design?<br />
Memorability: When users return to the design after a period <strong>of</strong> not using it, how easily<br />
can they re establish pr<strong>of</strong>iciency?<br />
Errors: How many errors do users make, how severe are these errors, <strong>and</strong> how easily can<br />
they recover from the errors?<br />
Satisfaction: How pleasant is it to use the design?<br />
Usability is <strong>of</strong>ten associated with the functionalities <strong>of</strong> the product, in addition to being<br />
solely a characteristic <strong>of</strong> the user interface (cf. framework <strong>of</strong> system acceptability, also<br />
below, which separates usefulness into utility <strong>and</strong> usability). For example, in the context<br />
<strong>of</strong> mainstream consumer products, an automobile lacking a reverse gear could be<br />
considered unusable according to the former view, <strong>and</strong> lacking in utility according to the<br />
latter view.<br />
When evaluating user interfaces for usability, the definition can be as simple as "the<br />
perception <strong>of</strong> a target user <strong>of</strong> the effectiveness (fit for purpose) <strong>and</strong> efficiency (work or<br />
time required to use) <strong>of</strong> the <strong>Interface</strong>". Each component may be measured subjectively<br />
against criteria e.g. Principles <strong>of</strong> <strong>User</strong> <strong>Interface</strong> <strong>Design</strong>, to provide a metric, <strong>of</strong>ten<br />
expressed as a percentage.<br />
It is important to distinguish between usability testing <strong>and</strong> usability engineering.<br />
Usability testing is the measurement <strong>of</strong> ease <strong>of</strong> use <strong>of</strong> a product or piece <strong>of</strong> s<strong>of</strong>tware. In<br />
contrast, Usability Engineering (UE) is the research <strong>and</strong> design process that ensures a<br />
product with good usability.<br />
Usability is an example <strong>of</strong> a non-functional requirement. As with other non-functional<br />
requirements, usability cannot be directly measured but must be quantified by means <strong>of</strong><br />
indirect measures or attributes such as, for example, the number <strong>of</strong> reported problems<br />
with ease-<strong>of</strong>-use <strong>of</strong> a system.<br />
The key principle for maximizing usability is to employ iterative design, which<br />
progressively refines the design through evaluation from the early stages <strong>of</strong> design. The<br />
evaluation steps enable the designers <strong>and</strong> developers to incorporate user <strong>and</strong> client<br />
feedback until the system reaches an acceptable level <strong>of</strong> usability.<br />
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