PDF of this tutorialManaging the Prototyping Process
The two main challenges with a prototyping approach are, first, ensuring that each prototype is an improvement over the previous version and, second, knowing when to stop. In order to manage these issues, it is important to set minimum and desirable usability performance targets as well as cut-off dates for iteration.
Figure 4. Usability Evaluation
Usability targets should correspond to the key scenarios that have been articulated. The actual values will be based on comparison with competitors' products, with previous versions of the product, or perhaps with the manual performance of a task that is being automated. Usability targets may be at different levels of detail (see examples).
Each usability target should include the following:
- the target users (stereotypes)
- the task or activity being carried out
- the relevant product features
- relevant aspects of the environment
Two Example Usability Targets
"Target market segments must be able to make their first telephone call within five minutes of opening the product packaging in the home."
"A network manager with at least two years experience, and with no measurable red-green visual deficiency, must be able to detect 99 percent of critical errors represented by color change from [rgb values to be defined] of a one-pixel-wide line connecting nodes on a visual display [specify makes], in lighting conditions representative of operations center X, over a one-hour period of typical peak hour traffic."
The Usability Trial
A prototyping approach allows the usability metrics to be monitored constantly, from the moment that the relevant product feature has been included until the desired target has been reached. In a typical usability trial, which is usually recorded on video, users will be asked to carry out specified critical tasks. The session may conclude with a questionnaire or debriefing interview. Typical usability targets will refer to time of completion of a task, number of errors made, or quality of completed task. The usability trial, however, is also an opportunity to obtain users' subjective reactions to the prototype and to follow up on marketing issues where appropriate.
Usability trials often take place in laboratory conditions when the measures must be precise and the environmental conditions carefully controlled. However, field tests will more accurately reflect the end use situation.
Implementation
The heart of the user-centered usability engineering process is the cycle between prototyping and evaluation. However, sooner or later—ideally triggered by achieving the usability targets—the product is implemented and there is a greater investment in packaging, marketing, production, selling, and maintenance.
Implementation can be seen as an evolution of the prototype-evaluation cycle, moving out of the development laboratory and into the marketplace. Every product can be seen as a set of hypotheses with the ultimate test of success being profitability.
In theory, all key issues should have surfaced during the previous design activities. There are always last-minute trade-offs to be made in implementation, however, and surprises that only emerge when a product finally goes to market. At least with a user-centered design approach, these further trade-offs can be made while keeping in mind the user priorities outlined earlier in the process.
Continuing the product evaluation activities post-launch will also help capture any surprise issues as soon as possible and give quick feedback for the next version of the product.
Post-launch there are also rich new sources of data to be exploited from the sales force, retail, and distribution channels, from trade reviews and user groups, from maintenance engineers, and from customer help-lines.
Figure 5. Implementation
Project Post-Mortems
Project post-mortems are not frequently carried out, but should be viewed as an opportunity to answer questions such as the following:
- Did the product really meet the targets?
- Were these the right targets?
- What trends will change the targets for the next generation?
- What are the unexpected field issues?
- What are the key manufacturing and distribution issues?
Project post-mortems and the continuation of the prototype-usability evaluation cycle into the marketplace improve the design process on its next cycle.
