Usability Concepts (Ch 8.1)

1. Usability Concepts (Ch 8.1) Yonglei Tao School of Computing & Info Systems GVSU

2. The Butterfly Ballot in 2000 Election

3. The Butterfly Ballot (Cont.)

4. The Butterfly Ballot (Cont.)

5. Usability • ISO Standard 9241-11 (1998) Guidance on Usability the extent to which a product can be used by specified users to achieve specified goals with effectiveness, efficiency and satisfaction in a specified context of use

6. Usability Attributes • Ease of learning • Efficiency of use • Memorability • User retention over time • Error frequency and severity • SubjectiveSatisfaction

7. Typical Usability Measurements • User’s self-assessment on a scale • User’s years of training or number of courses taken • User’s score on a comprehensive test that is given after learning the system. • Number of errors on a standard task. • Time to complete a standard task. • Number of standard tasks completed in a set time period • Number of features used

8. A Case Study • Usability test on redesign of two existing screens • from NASA’s Space Shuttle Guidance, Navigation, and Control subsystem • Data from a search task • 31% improvement in search time and 28% reduction in errors by novice users • some improvement in performance by expert users • Observations • importance of making the right screen design decisions • certain techniques provide advantages for first-time user over other techniques

9. Aspects of Redesign • Captions were provided for all data fields • Related data were grouped together • Consistency in the placement of certain items was introduced • The menu selection techniques was changed from number codes to cursor selection to avoid confusion between selection codes and other numerical fields • Indentation and underlying were introduced to reinforce for captions • Captions were changed to be more clear • A consistent abbreviation scheme was introduced for captions • Numerical data were decimal aligned

10. Other Reports • Study 1 • Reformatting inquiry screens based on good design principles reduced decision-making time by about 40%, resulting in a savings of 70 person-years in the affected system • Study 2 • By comparing 500 screens, it was found that the time to extract information from displays of airline or lodging information was 128% faster for the best format than for the worst • Study 3 • Training costs are lowered because of training time is reduced, support line costs are lowered because fewer assist calls are necessary, and employee satisfaction is increased because aggravation and frustration are reduced.

11. Guidelines from Companies • Macintosh Human Interface Guidelines • Emphasizes the importance of the user’s ability to perform actions by choosing from alternatives presented on the screen, as opposed to having to “remember any particular command or name.” • IBM CUA Guide • “The designer should approach application design with a ‘no user errors’ philosophy. The user should feel that any shortcomings are in the application, not in himself or herself.”

12. Guidelines (Cont.) • NeXTSTEP User Interface Guidelines • “When working in an application, the user should be afforded the widest possible freedom of action. It is inappropriate for an application to arbitrarily restrict what the user can do. If an action makes sense, it should be allowed.” • Guidelines for Microsoft Windows • “Application should always be as interactive as possible. The user should not have to wait a long time for processing to be completed.”

13. Guidelines (Cont.) • OSF/Motif Study Guide • “Each screen object needs to have a distinct appearance that the user can easily recognize and understand.” • “Appropriate use of contrast helps the user distinguish screen objects against the background of a window. Very dark screen objects on a light background, very bright objects on a dark background, and bright colors all command the user’s attention.”

14. Guidelines (Cont.) • Macintosh Human Interface Guidelines • “People need to feel that they can try things without damaging the system; create safety nets for people so that they feel comfortable learning and using your product.” • “Always warn people before they initiate a task that will cause irretrievable data loss.” • IBM CUA Guide • “If an action cannot be made reversible, the application should display a message advising the user of the condition and suggest alternative actions the user might take to avoid irreversible negative consequences.”

15. U.S. Military Standard • For Human Engineering Design Criteria (1999) states these purposes: • Achieve required performance by operator, control, and maintenance personnel • Minimize skill and personnel requirements and training time • Achieve required reliability of personnel-equipment/software combinations • Foster design standardization within and among systems

16. Quotes from “Asynchronous UIs” by Alex MacCaw Speed matters a lot. Or to be precise, perceived speed matters a lot. Speed is a critical and often neglected part of UI design, but it can make a huge difference to user experience, engagement and revenue. • Amazon: 100 ms of extra load time caused a 1% drop in sales (source: Greg Linden, Amazon). • Google: 500 ms of extra load time caused 20% fewer searches (source: Marrissa Mayer, Google). • Yahoo!: 400 ms of extra load time caused a 5–9% increase in the number of people who clicked “back” before the page even loaded (source: Nicole Sullivan, Yahoo!).