1. Importance of Usability How can usability have impact on user attitude? How can usability affect sales of the software? How can usability affect workplace productivity? How can usability affect safety? 2. Satisfaction vs. Performance Relative importance of satisfaction vs. performance Neilson & Levy ( "Measuring Usability - Preference vs. Performance") findings How to design for satisfaction 3. Why Users Have Problems with Interfaces Mack et al (1987) and Carroll & Mack (1987) established how people learn to use software and what the problems are (1) Learning is difficult and is personalized (2) Learners lack basic knowledge (3) Learners make ad hoc interpretations (4) Learners generalize from what they know (5) Learners have trouble following directions (6) Problems interact 3. What Errors Are Important to understand why errors occur Norman's (1981) work on errors in using software Two basic classes: mistakes slips Types of slips (elicit examples) Capture error: Description error: Data-driven error: Associative-activation error: Loss-of-activation error Mode error: What can be done to prevent slips? What can be done to prevent mistakes?