An Introduction to Usability (Patrick Jordan)
What is Usability?
Patrick Jordan defines the concept of 'usability' in the context of product development and interface design. Based on the International Standards Organisation's categories of "effectiveness, efficiency and satisfaction," the author determines ways in which usability can be quantified.
Effectiveness is the capacity for a product to generate (or enable) output;
Efficiency is measured as the level of effort invested in completing an action or task (for example, the author categorizes usability errors as distinguished between a 'slip' and a 'mistake' in user performance and experience. For him, a slip is when a user accidentally performs the wrong action, which is readily corrected by the user, whereas a mistake is when a user thinks he is doing the right thing (intuitive action), but is unable to perform his task. Errors can be minor, major, fatal, or catastrophic. Designing for Usability is to design products that ideally have very little errors or none.); and
Satisfaction, as a separate level of usability, is understood as how comfortable or 'at ease' one feels when using a product, which underlies what has been referred as "user-friendliness" (subjective values).
Those three considerations are important in guiding the design and features of affirmative usability.
In noting that 'usability' is now critical in determining whether or not a product is adopted or rejected, the author emphasizes audience 'expectation'. Hence, the importance of user-centeredness in design. For the author, 'usability' is when effectiveness, efficiency, and satisfaction are at their peak, and when those measures determine the ease of use and "interaction between a product, user and task." The author highlights key measures of user-centeredness; such as designing for: experience (first-time or frequent user experience determine a user's ability to make connections between different tasks of a given product, or between different product of a same kind), domain knowledge (interface fluency or technological knowledge), cultural background (when design is tailored to respond to cultural behaviour and physical characteristics — such as, colour references and ethnic features — then design is able to make product features more intuitive or explicit), disability (considers users with special needs and aims at creating products that include and accommodate universal use — such as disabled toilets, etc.), and age and gender (takes into account generational differences in technological abilities and attitude in general).
Jordan also lists measurable aspects of design when thinking of user-performance: 'Guessability', 'Learnability', 'Experienced User Performance' (EUP), 'System Potential', and 'Re-Usability'.
'Guessability' refers to how easily a task is understood at first hand (which the author calls a cost).
'Learnability' refers to how easily it is for a user to 'learn' how to use a product's features, which measures levels of user-performance (recognition, memorability, etc.).
EUP (similar to 'Learnability') refers to the need for products to provide higher levels of performance for more skilled or experienced users.
'System Potential' refers to the need for products to allow access to a product's maximum potential.
Finally, 'Re-Usability' is concerned with users who might leave a system for a certain amount to time. Re-Usability measures the easiness with which a product's tools are recalled.
10 Principles of Usable Design.
Here, the author presents 10 principles of usable design that describe the different elements in design that affect usability: 'Consistency', 'Compatibility', 'Consideration of User Resources', 'Feedback', 'Error Prevention and Recovery', 'User Control', 'Visual Clarity', 'Prioritisation of Functionality and Information', 'Appropriate Transfer of Technology', and 'Explicitness'.
'Consistency' enables users to generalize task requirements across different products or different tasks ("Inconsistencies are likely to lead to errors.").
'Compatibility' is the potential of design to mean user understanding, expectation, and ability.
'Consideration of User Resources' guides design with regard to the bodily language of hands, eyes, ears, etc., by using sound, visual cues, and tactile functions.
'Feedback' refers to systems that indicate an action has been made.
'Error Prevention and Recovery' facilitate the recovery from user errors by walking people through an exit path or by giving users the possibility to go back in time (i.e. 'undo').
'User Control' is enhanced by providing 'adjustable' or customizable features, which in turn emphasize user-centeredness.
'Visual Clarity' considers scale, location and distance (i.e., buttons are labelled, interfaces are at proximal distances and located in convenient, readily accessible ways).
'Prioritisation of Functionality and Information' focuses on the hierarchy of information of tools (IA): this measure becomes subject to error when products contain clustered information or features.
'Appropriate Transfer of Technology' takes into account the surrounding environment (context) of transferring or crossing different systems to enhance one or the other with regard to safety measures.
Finally, 'Explicitness' coincides with Don Norman's concept of 'affordances' wherein product displays provide perceptible clues as to what they are used for and how they operate.
This text offers a range of considerations for designing for usability, which entails designing for user experience, user performance and safety, in terms of effectiveness, efficiency, and satisfaction. It helps designers focus on user-centredness when thinking of usability and provides them with a vocabulary for investigating and measuring the success of their outputs.
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