Appliance Design - September 2008 - (Page 24) INDUSTRIAL DESIGN & HUMAN FACTORS through guidelines and measurements, or even better, by averaging observed user performance with similar systems. Values can vary widely based on the factors such as the user’s level of experience with such an interface, so models need to be appropriately qualified. With these behavioral times, one can sum the discrete steps a user executes when completing particular tasks, and compare the total time across different interfaces. For example, completing a particular task with one version of an interface might require the following sequence of steps: c, d, a (8 seconds). An alternative might require a different set of actions: a, e, b, c, d, a (12.25 seconds). In this example, the first interface was less complex with respect to both task time and numbers of steps. (There are specialized software applications that assist with this type of interface modeling, such as CogTool from Carnegie Mellon University.) There are some obvious trade-offs to the modeling approach. On the positive side, it provides a consistent method for quantifying and comparing the complexity of two interfaces with respect to the time required to complete tasks. The approach is helpful for quickly evaluating concepts or prototypes against legacy and competitor products, particularly for complex, multi-step interactions, without involving end-users. Its primary limitations are that it oversimplifies the situation and does not accommodate any of the variability inherent in human experience. Consider also that one interface may require a user to take more time and steps than another, but still be perceived as more usable due to other factors such as the tone or visual presentation of the information. Examples include recently developed gesture-based interfaces that employ intuitive user interactions, such as those found on the iPhone. It may take longer to scroll through an alphabetical list of options with your fingers compared to typing a keypad shortcut, but the ease of interaction and mild learning curve impact the perceived ease of use, as opposed to simply a timebased metric. Fortunately, usability testing provides a much more robust and valid way for determining the complexity of the user experience. During usability testing, representative end-users conduct tasks using existing products, prototypes, or concepts. The level of realism in a prototype depends on the tasks and measures being considered. For example, choosing the correct item from a printed list of menu choices is largely comparable to doing the same on an electronic display if the focus is on the labeling and sequence of the choices. Using a paper list would not, however, be a good substitute for evaluating the readability of an electronic display in a low-light environment. In usability testing, typical metrics include task success or failure rate, the time to complete a task, and the types and frequencies of errors. In addition, qualitative participant ratings and feedback, along with researcher observations, provide depth and meaning to better understand the relative strengths and weaknesses of each alternative design. I recommend reviewing the recently published international standard on the Ease of Operation of Everyday Products (ISO 20282), which Automaker BMW recently redesigned the iDrive controls to better accommodate interaction in the context of driving. (Image: BMW.) QUALITY TO PROTECT PEOPLE LCDIs • GFCIs • ALCIs TOWER– LCDI GFCI ALCI • Customized to meet your specs • Priced from our own Asian plant to keep you competitive • Customer service from our USA headquarters for quick satisfaction 25 Reservoir Avenue, Providence, RI 02907 • Tel: 401-467-7550 • Fax: 401-461-2710 TOWERManufacturing Corporation www.towermfg.com September 2008 24 applianceDESIGN AD09074Tow2.indd 1 www.applianceDESIGN.com 8/2/07 10:28:44 AM http://www.towermfg.com http://www.appliancedesign.com
For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.