Human Factors and Usability
by B. Shackel

During the eighties the man power invested in human factors research by American companies increased rapidly. This, as well as a growth in numbers of books, journal and conferences dedicated to this area of research, shows that there is a focus of attention of these issues. Shackel questions the results of these efforts. He thinks that much of the research fails to lead to desired results. According to him, we need a deeper understanding of the psychological aspects of man-machine interfaces before the problem of how the interactions should be conducted can be resolved. Shackel also considers design tools and methodology as well as the issue of interaction to be especially important.

Instead of trying to find a good method of design for usability we have to find out what usability is. The four components of any user situation is: user, task, system and environment. To achieve usability is to achieve harmony between these components. In his search for a definition of usability Shackel has come across a number of attempts. He has then tried to merge these together into one framework called usability design. These are the emergent properties of the five fundamental features.

• User-centred design
  It is of course important for the designer to know who the users will be and what tasks they will perform. This requires contact with the users. Preferably the designer should learn at least some of the tasks that the system will support. The design must start with the creation of a usability specification.
• Participative design
  A group of future users should co-operate with the design team. Mock-ups and simulations should be created whenever possible. If possible the interface manual should be written and tried out together with the mock-ups and simulations.
• Experimental design
  Trials should be conducted and evaluated as early as possible in the design process. Important parts of the system should be made in several different variations that the users can try and choose between.
• Iterative design
  The process of design, test, measure and redesign has to be iterated until the demands of the usability specification has been met.
• User supportive design
  Documentation and interactive help should be developed concurrently with the rest of the system.