13. The sooner formative evaluation is conducted during development, the more likely that substantive improvements will be made and costly errors avoided (Reeves & Hedberg, 2003, p. 142).
26. “at least 90% of all commercial Web sites are overly difficult to use….the average outcome of Web usability studies is that test users fail when they try to perform a test task on the Web. Thus, when you try something new on the Web, the expected outcome is failure.” —Jakob Nielsen
39. Ease of learning - How fast can a user who has never seen the user interface before learn it sufficiently well to accomplish basic tasks?
40. Efficiency of use - Once an experienced user has learned to use the system, how fast can he or she accomplish tasks?
41. Memorability - If a user has used the system before, can he or she remember enough to use it effectively the next time or does the user have to start over again learning everything?
42. Error frequency and severity - How often do users make errors while using the system, how serious are these errors, and how do users recover from these errors?