Thinking Out of the Box

User Interface Prototypes in Usability Engineering

Markus Weber
Markus Weber
August 25th, 2009

User interface prototyping is an essential activity in the field of user interface design that provides a basis for continuous evaluation and improvement of a to-be-designed user interface. In usability engineering, the focus of using prototypes lies on evaluating the usability of intended approaches and on generating concrete recommendations for advancing an interface design. While doing so, there are several aspects to keep in mind in order to maximize the efficiency of prototype use for usability engineering. Three issues are described in this post.

Level of Detail

Visual and functional aspects of a prototype can be implemented anywhere on the spectrum between low fidelity and high fidelity by either only sketching visual aspects and functionality or by implementing them in high detail.

The usability engineer should be aware of the fact that the level of visual detail can significantly impact the type and direction of feedback that participants in a usability test provide, especially the explicit verbal feedback (e.g. provided in post-test interviews). A prototype displaying a high level of visual detail can lead to a large proportion of comments regarding the visual design of the respective user interface while the proportion of feedback that is relevant for evaluating the interaction design is low. On the other hand, while high fidelity can lead participants in a usability test on the wrong track, it should also be noted that the fidelity of a prototype can be too low – in that case the prototype does not engage participants enough to provide relevant feedback.

It is the usability engineer’s task to care for the appropriate match of evaluation focus and prototype fidelity. In addition, he should monitor the feedback participants provide during a testing session with the prototype (or post-test interviews) and, if necessary, carefully intervene when he realizes that participants get “derailed” and provide too much feedback that is not relevant for the focus of the evaluation.

Interactions and Workflows

The user interface of an interactive system supports the user in completing workflows and carrying out interactions. Roughly speaking, workflows are sets of individual steps that serve an overarching goal, whereas interactions are smaller entities that can be part of several workflows.

Not all kinds of prototypes are equally suited for evaluating those interactions; paper prototypes usually lack the required level of interactivity. They often are, however, convenient tools for investigating workflows, e.g. by simulating screen flows for a participant to walk through. If the focus shall be set on evaluating details of interacting with certain UI widgets/controls, which can also have an impact on overall user experience, more advanced HTML-, Java- or other types of prototypes can be used, in which at least the controls in question are implemented in a more high-fidelity fashion.

It is therefore the usability engineer’s responsibility to ensure the optimal match of type/fidelity of the prototype and focus of the examination to guarantee an efficient data collection.

Expectation Management

Quite often, a prototype is presented to parties that are not part of the project team, e.g, during usability tests or board meetings. Inevitably, being confronted with a prototype leads to certain impressions and expectations with the respective audience.

A high fidelity prototype can lead an audience to the assumption that the system in question is nearly completed and will be rolled out soon. In addition, participants may not abstract from existing bugs of the prototype and perceive them as defects of the system in question. Factors like these can become especially problematic when a usability test is conducted internally in an organization with future users of the system: the internal project manager may be faced with considerable pressure if he fails to set expectations appropriately.

It is important for the usability engineer to actively manage expectations of the respective audience in order to avoid detrimental effects. This can, e.g., take the form of explaining that the prototype is merely an artifact for a project purpose such as a usability test, which is subject to change. The remark that errors can occur during interaction with the prototype, which is often made in usability tests, is also part of expectation management.

Collaborating with Software Developers

A close collaboration of usability engineers with software developers can be helpful to maximize efficiency of prototype usage in the user interface design process.

When prototypes created by software developers include parts of the user interface and functionality / interactions that are relevant for a usability test, a re-use may be possible without investing too much additional effort. With new tools for user interface design such as Microsoft® Expression Blend™ and Adobe® Flash® Catalyst™, re-use may also happen the other way round with developers benefiting from interactive prototypes created by usability engineers and user interface designers.

The usability engineer often has access to information about business logic that may be helpful for developers in order to simulate realistic data-environments and data manipulations for their prototypes.
Finally, a concerted expectation management of usability engineer and software developers can help to set the appropriate expectations with end users and management, which, in turn, contributes to avoiding unnecessary project pressure due to unrealistic expectations.


Further reading: Additional information on the topic (including the developer perspective) can be found in: Weber, M. & Immich, T. (2008). User Interface Prototypen in Usability Engineering und Software Entwicklung: Probleme und Synergien. In H. Brau, S. Diefenbach, M. Hassenzahl, F. Koller, M. Peissner & K. Röse (Hrsg.), Usability Professionals 2008 (S. 40-44). Stuttgart: German Chapter der Usability Professionals Association e.V.

Microsoft and Expression Blend are either registered trademarks or trademarks of Microsoft Corporation in the United States and/or other countries.

Adobe, Flash and Flash Catalyst are either registered trademarks or trademarks of Adobe Systems Incorporated in the United States and/or other countries.

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