An effective user-centered design process involves a number of important phases: designing, prototyping, testing, and iterating. The following sections describe these phases.
The initial work on a software's design can be the most critical because, during this phase, you decide the general shape of your product. If the foundation work is flawed, it is difficult to correct afterwards.
This part of the process involves not only defining the objectives and features for your product, but understanding who your users are and their tasks, intentions, and goals. This includes understanding factors such as their background — age, gender, expertise, experience level, physical limitations, and special needs; their work environment — equipment, social and cultural influences, and physical surroundings; and their current task organization — the steps required, the dependencies, redundant activities, and the output objective. An order-entry system may have very different users and requirements than an information kiosk.
At this point, begin defining your conceptual framework to represent your product with the knowledge and experience of your target audience. Ideally, you want to create a design model that fits the user's conceptual view of the tasks to be performed. Consider the basic organization and different types of metaphors that can be employed. Observing users at their current tasks can provide ideas on effective metaphors to use.
Document your design. Committing your planned design to a written format not only provides a valuable reference point and form of communication, but often helps make the design more concrete and reveals issues and gaps.
After you have defined a design model, prototype some of the basic aspects of the design. This can be done with "pencil and paper" models — where you create illustrations of your interface to which other elements can be attached; storyboards — comic book-like sequences of sketches that illustrate specific processes; animation — movie-like simulations; or operational software using a prototyping tool or normal development tools.
A prototype is a valuable asset in many ways. First, it provides an effective tool for communicating the design. Second, it can help you define task flow and better visualize the design. Finally, it provides a low-cost vehicle for getting user input on a design. This is particularly useful early in the design process.
The type of prototype you build depends on your goal. Functionality, task flow, interface, operation, and documentation are just some of the different aspects of a product that need to be assessed. For example, pen and paper models or storyboards may work when defining task organization or conceptual ideas. Operational prototypes are usually best for the mechanics of user interaction.
Consider whether to focus your prototype on breadth or depth. The broader the prototype, the more features you should try to include to gain an understanding about how users react to concepts and organization. When your objective is focused more on detailed usage of a particular feature or area of the design, use depth-oriented prototypes that include more detail for a given feature or task.
User-centered design involves the user in the design process. Usability testing a design, or a particular aspect of a design, provides valuable information and is a key part of a product's success. Usability testing is different than quality assurance testing in that, rather than find programming defects, you assess how well the interface fits user needs and expectations. Of course, defects can sometimes affect how well the interface will fit.
There can be different reasons for testing. You can use testing to look for potential problems in a proposed design. You can also focus on comparative studies of two or more designs to determine which is better, given a specific task or set of tasks.
Usability testing provides you not only with task efficiency and success-or-failure data, it also can provide you with information about the user's perceptions, satisfaction, questions, and problems, which may be just as significant as the ability to complete a particular task.
When testing, it is important to use participants who fit the profile of your target audience. Using fellow workers from down the hall might be a quick way to find participants, but software developers rarely have the same experience as their customers. The section, "Usability Assessment in the Design Process," provides details about conducting a usability test.
Because testing often uncovers design weaknesses, or at least provides additional information you will want to use, repeat the entire process, taking what you have learned and reworking your design or moving onto reprototyping and retesting. Continue this refining cycle through the development process until you are satisfied with the results.
During this iterative process, you can begin substituting the actual application for prototypes as the application code becomes available. However, avoid delaying your design cycle waiting for the application code to be complete enough; you can lose valuable time and input that you could have captured with a prototype. Moreover, by the time most applications are complete enough for testing, it is difficult to consider significant changes, because it becomes easier to ignore usability defects because of the time resources invested. In addition, changes at this point may affect the application's delivery schedule.