The contextual nature of usability and its relevance to medical informatics.

We report from three usability evaluations of health information systems that illustrate the value of seeing usability as a context dependent property of a product. We show how the definition of usability in ISO 9241-11 can be used as a guiding principle in the evaluation, specification and design of such systems. The contextual view on usability is particularly important for health information systems because of their great diversity concerning user groups, tasks, and work environments.