Evaluation is a fundamental part of human-computer interaction (HCI). Good HCI practice tells designers to evaluate: evaluate requirements, evaluate designs, evaluate prototypes. The purpose of evaluation is to improve the usability of a software system; that is to make it easy to use, easy to learn, effective and enjoyable. But what is usability and what makes one device easier to use than another? Traditional HCI theory has produced a number of evaluation techniques and guidelines. These are based on some basic psychological assumptions which date back to the sixties.
Benyon, David. ERCIM News (2001). Articles>Human Computer Interaction>Information Design