As human short-term working memory capacity is limited, a
website should be capable to eliminate or reduce the working
memory overload associated to the need to mentally retain and
integrate several pieces of information and knowledge, but, at the
same time, to provide the user with a pleasant and satisfying
experience (Sweller, 1994). Cognitive efficiency, then, may be an
effective measure of how much cognitive work the users have to
perform outside of their working memory in a given task, given the
constraining nature of the website interfaces. The theories of
cognitive efficiency suggest that, when the user cognitive tasks can
be performed easily and quickly, the cognitive effort can be minimized
and the search performance and the user gratification can be
maximized. If information is almost processed automatically with
the support of the website, the user cognitive efficiency may substantially
increase. Thus, better websites allow the user to have a
greater cognitive efficiency during interaction. Following this discussion,
an efficiency index can be constructed, by considering the
ratio of the user perceived cognitive benefits to cognitive costs
incurred during the interaction with the website