Usability is a concept that can be applied to the analysis and design for a range of products which defines how easy they are to use. The British Standard/ISO Standard: Human Centred design processes for interactive systems defines usability as the:
extent to which a product can be used by specified users to achieve specified goals with effectiveness, efficiency and satisfaction in a specified context of use.
An analysis of an existing site or prototype, by an experienced usability expert who will identify deficiencies and improvements to a site based on their knowledge of web design principles and best practice.
Representative users are observed performing representative tasks using a system.
You can see how the concept can be readily applied to web site design - web visitors often have defined goals such as finding particular information or completing an action such as booking a flight or viewing an account balance.
In Jakob Nielsen's classic book Designing Web Usability (Nielsen, 2000b), he describes usability as follows.
An engineering approach to website design to ensure the user interface of the site is learnable, memorable, error free, efficient and gives user satisfaction. It incorporates testing and evaluation to ensure the best use of navigation and links to access information in the shortest possible time. A companion process to information architecture.
In practice, usability involves two key project activities. Expert reviews are often performed at the beginning of a redesign project as a way of identifying problems with a previous design. Usability testing involves:
1 Identifying representative users of the site (see, for example, Table 7.3) and identifying typical tasks;
2 Asking them to perform specific tasks such as finding a product or completing an order;
3 Observing what they do and how they succeed.
For a site to be successful, the user tasks or actions need to be completed:
• Effectively - web usability specialists measure task completion, for example, only 3 out of 10 visitors to a web site may be able to find a telephone number or other piece of information.
• Efficiently - web usability specialists also measure how long it takes to complete a task on-site, or the number of clicks it takes.
Jakob Nielsen explains the imperative for usability best in his 'Usability 101' (www.useit.com/alertbox/20030825.html). He says:
On the Web, usability is a necessary condition for survival. If a website is difficult to use, people leave. If the homepage fails to clearly state what a company offers and what users can do on the site, people leave. If users get lost on a website, they leave. If a website's information is hard to read or doesn't answer users' key questions, they leave. Note a pattern here?
For these reasons, Nielsen suggests that around 10% of a design project budget should be spent on usability, but often actual spend is significantly less.
Some would also extend usability to include testing of the visual or brand design of a site in focus groups, to assess how consumers perceive it reflects the brand. Often, alternative visual designs are developed to identify those which are most appropriate.
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