Usability is an important consideration in the design of products because it is concerned with the extent to which the users of products are able to work effectively, efficiently and with satisfaction.
Usable products may be designed by incorporating product features and attributes known to benefit users in particular contexts of use. This processalone is not sufficient to ensure that the product will be effective, efficient and satisfying in use. In order to establish the level of usability achieved, it is necessary to measure the performance and satisfaction of users working with a product. Measurement of usability is particularly important in view of the complexity of the interactions between the user and the task characteristics and the other elements of the context of use, which can result in significantly different levels of usability for the same product when used in different contexts.
Dealing with usability as part of a quality system for design and development of products, as specified in ISO 9001, involves the systematic identification of requirements for usability, including usability measures and verifiable descriptions of the context of use. These provide design targets which can be the basis for verification of the resulting design.
The approach adopted in this part of ISO 9241 has benefits which include:
- The framework identifies the aspects of usability and the components of the context of use to be taken into account when specifying, designing or evaluating the usability of a product.
- The performance and satisfaction of the users provide direct measures of whether a product is usable in a particular context.
- Measures of the performance and satisfaction of the users provide a basis for the comparison of the relative usability of products with different technical characteristics which are used in the same context. (This is the principle on which the performance tests being developed for ISO 9241 Parts 3 and 4 are based).
- The usability of a product can be defined, documented and verified as part of a quality system which conforms to ISO 9001.