ABSTRACT
This chapter defines usability various components and discusses the various measures by which usability can be quantified. Effectiveness refers to the extent to which a goal, or task, is achieved. In some cases, the distinction between a task being achieved successfully or not may simply be success or failure in that task. Satisfaction refers to the level of comfort that the users feel when using a product and how acceptable the product is to users as a means of achieving their goals. This is a more subjective aspect of usability than effectiveness or efficiency. A product that is usable for one person will not necessarily be usable for another. There are a number of user characteristics which can be predictors of how easy or difficult a product is to use for that person. New technology should also enable some products to be made more usable for those with special needs.
