Usability Testing

There are some obvious trade-offs to the modeling approach to usability testing. On the positive side, it provides a consistent method for quantifying and comparing the complexity of two user interfaces with respect to time to complete tasks. It is helpful for quickly new applications -- 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 user 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. Recent gestural interfaces that employ intuitive user interactions (like the iPhone) are examples of this situation. It may take longer to scroll through an alphabetical list of options with your fingers versus typing a keypad shortcut, but the ease of interaction and mild learning curve impact the perceived ease of use (as opposed to simply a time-based metric).

Fortunately, usability testing provides a much more robust and valid way for determining the complexity of users’ experiences. During usability testing representative end-users conduct tasks using existing products, prototype or concepts for new applications. 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, versus, the readability in a low-light environment. 

In usability testing, typical metrics include task success or failure rate, time to complete task, and 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 – especially important for usability testing for new applications. We recommended reviewing the recently published international standard on the Ease of Operation of Everyday Products (ISO 20282), which provides guidance and metrics for usability testing appliances.

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