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7.1. Relationship to usability Measures of usability apply to products used within the overall work system. Measures of effectiveness, efficiency and satisfaction can be used to evaluate how any component of a work system affects the quality of the whole work system in use. If the aim is to improve the quality of the overall work system in use, any part of the work system may be the subject of design or evaluation. For example it may be appropriate to consider the amount of user training to be provided, changes in lighting, or re-organisation of the task. In this case the element which is the object of design or evaluation is considered to be subject to potential variation, while the other elements of the work system are treated as fixed. 7.2. Examples of application 7.2.1. Design of a complete work system When designing a complete work system its quality in use may be optimised by changing components of the context of use of a product, such as the operating system, lighting or amount of user training. In this case measures of effectiveness, efficiency and satisfaction can be used to specify or evaluate the effect of different operating systems, different types of lighting, or different amounts of user training respectively. 7.2.2. Diagnostic evaluation When the quality of a work system in use is recognised to be unsatisfactory it is often necessary to carry out systematic analyses of the contribution of different components of the context of use and the interactions between them, in order to determine what the principle causes of the problems are. This process may also be used to identify which components are amenable to change, in order to bring about improvements in the quality of the work system in use. Diagnostic activity relating to the context of use is often a necessary step in the specification and evaluation of product usability, since it provides the basis for judging whether problems can be resolved by the re-design of the product.
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