The definition of user profile is important in a user study. And so is also a task analysis attempting to state the needs, e.g. what the user/operator is actually going to do with the product/system in question. The objective of ergonomics is to achieve the best possible match between the product and its users in the context of both the (working) task ( Pheasant 1996) and the whole contextual system. An effective user study is an important basic tool for preventing mismatch, and hence for promoting usability. Ergonomic usability studies help to elaborate the concepts initially identified through a requirement analysis supported by user studies (Fig. 2).
Design iterations are often needed in addition to the initial usability studies of the first prototype. Thus, iteration, often with "rapid prototyping", is an essential feature of modern user-centred design. A user trial is an experimental investigation in which a group of users tests versions of the product under