One of the outputs of the requirements gathering stage of the UCD is an inventory of the problems that users commonly encounter in the course of their tasks with the interface. Flowever, users may not be able to clearly articulate a specific problem. To accompany the user-generated list of usability issues, it is helpful for the evaluator to inspect the interface to compare against a list of well-known design guidelines or heuristics. This advice is not specific to testing older users, but it does especially help when involving them in usability testing, to provide references or touch- points for the design of future displays.

Heuristic evaluations

Heuristic evaluation is a method of quickly assessing a user interface or system for its adherence to a set of pre-defined usability principles (Table 6.3). Heuristic evaluations are popular because of their ease of use and low cost (no special equipment is required). A set of evaluators (three to five) compare an interface against a list of usability heuristics and note any violations of the usability principles. The evaluators then gather to discuss and rank each problem in terms of severity. Heuristic evaluations can be specific to the type of system being evaluated (e.g., heuristics for mobile phone interface design, game design).

Although the heuristics are well researched, additional consideration of them or additional heuristics may be generated and used for specific kinds of systems or even specific user groups. However, extra attention should be devoted to the fact that criteria for what may constitute a heuristic violation may be different for older adults than for younger adults. For example, consider the first of Nielsen's heuristics (visibility of system status). Visibility includes feedback about what has just happened, where one is in the interface or display or task, and what options are available (and which are encouraged). The heuristic states that feedback should be given in a reasonable amount of time, but what is reasonable for younger adults may be much too short for older adults not only because of perceptual deficits but also because of attentional constraints they may not be attending to the proper location at exactly the right time. A rich set of heuristics specific to older web users have been developed by Dana Chisnell and colleagues. The reference to their heuristics is available at the end of this chapter.

6.4 Designing/prototyping/

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