Usability of interactive systems. Usability requirements

Transcription

1 Usability of interactive systems Human-Computer Interaction Fall 2009 I VP R 1 Usability requirements Synonyms for user-friendly (Microsoft Word 2002) easy to use Accessible Comprehensible Intelligible idiot proof Available ready I VP R 2

2 But friend also seeks to help + be valuable not only understandable but understands reliable doesn t hurt pleasant to be with I VP R 3 Subjective, vague measures need systematic process to develop usable systems for specific users in specific context I VP R 4

3 Usability requirements (cont.) U.S. Military Standard for Human Engineering Design Criteria (1999) purposes: I VP R 5 Achieve required performance by operator, control, and maintenance personnel Minimize skill and personnel requirements and training time Achieve required reliability of personnelequipment/software combinations Foster design standardization within and among systems I VP R 6

4 quality of life improving user s quality of life community also objectives? I VP R 7 Usability requires project management careful attention to requirements analysis testing for clearly defined objectives I VP R 8

5 Goals for requirements analysis Ascertain user s needs ensure reliability promote standardization integration consistency portability I VP R 9 Goals (cont.) Complete projects on time within budget I VP R 10

6 Ascertain user s needs tasks &subtasks to be carried out include occasionally-performed common tasks easy to identify functionality match need or users reject / underutilize I VP R 11 Ensure reliability actions function as specified DB data displayed reflect actual DB appease user's sense of mistrust system available as often as possible system must not introduce errors Ensure user's privacy and data security protect against unwarranted access, destruction of data, malicious tampering I VP R 12

7 standardization, integration, consistency, portability I VP R 13 Standardization use pre-existing industry standards where exist aid learning avoid errors e.g. W3C ISO standards I VP R 14

8 Integration product able to run across different software tools and packages (e.g. Unix) I VP R 15 Consistency compatibility across different product versions with related paper other non-computer based systems use common action sequences, terms, units, colors, etc. within program I VP R 16

9 Portability allow user to convert data across multiple software & hardware environments I VP R 17 Goals for requirements analysis Complete projects on time and within budget Late / over budget products serious pressure within company potentially dissatisfied customers loss of business to competitors I VP R 18

10 Usability measures Define target user community class of tasks associated with interface Communities evolve and change e.g., interface to information services for U.S. Library of Congress I VP R 19 5 human factors central to community evaluation: I VP R 20

11 Time to learn How long for typical members of community to learn relevant task? I VP R 21 Speed of performance How long to perform relevant benchmarks? I VP R 22

12 Rate of errors by users How many what kinds errors made during benchmark tasks? I VP R 23 Retention over time Frequency of use ease of learning help make for better user retention I VP R 24

13 Subjective satisfaction user feedback interviews free-form comments satisfaction scales I VP R 25 Usability measures (cont.) Trade-offs in design options frequent Changes to interface in new version may create consistency problems with previous version, but improve interface in other ways or introduce new needed functionality I VP R 26

14 Design alternatives evaluated by designers and users mockups / high-fidelity prototypes basic tradeoff : get feedback early less expensive in development process vs more authentic interface evaluated I VP R 27 Usability motivations Many interfaces poorly designed across domains: I VP R 28

15 Life-critical systems Air traffic control, nuclear reactors, power utilities, police & fire dispatch systems High costs, reliability & effectiveness expected Lengthy training periods acceptable despite financial cost error-free performance avoid low frequency but high cost errors Subject satisfaction less issue well motivated users I VP R 29 Usability motivations (cont.) I VP R 30

16 Industrial and commercial uses Banking, insurance, order entry, inventory management, reservation, billing, point-of-sales systems Ease of learning important to reduce training costs Speed and error rates relative to cost Speed of performance important number of transactions Subjective satisfaction fairly important limit operator burnout I VP R 31 Usability motivations (cont.) I VP R 32

17 Office, home, entertainment applications Word processing electronic mail computer conferencing video game systems educational packages, search engines mobile device etc. I VP R 33 Ease of learning low error rates subjective satisfaction paramount use often discretionary competition fierce I VP R 34

18 Infrequent use of some application interfaces must be intuitive easy to use online help important I VP R 35 Choosing functionality difficult wide range user population novice expert Competition need for low cost I VP R 36

19 Usability motivations (cont.) I VP R 37 Exploratory, creative, and cooperative systems Web browsing search engines artist toolkits architectural design software development music composition scientific modeling systems I VP R 38

20 Collaborative work I VP R 39 Benchmarks hard to describe for exploratory tasks device users I VP R 40

21 computer should "vanish" user absorbed in task domain I VP R 41 Usability motivations (cont.) I VP R 42

22 Social-technical systems Complex systems involve many people over long time periods I VP R 43 e.g., Voting health support identity verification crime reporting I VP R 44

23 issues Trust privacy responsibility security I VP R 45 important! Verifiable sources status feedback I VP R 46

24 need Ease of learning for novices feedback to build trust I VP R 47 Administrators need tools to detect unusual patterns of usage I VP R 48

25 Universal Usability I VP R 49 Physical abilities and physical workplaces anthropometry Basic data about human dimensions I VP R 50

26 no average user either compromises made or multiple versions of system created I VP R 51 Physical measurement of human dimensions not enough take into account dynamic measures such as reach strength speed I VP R 52

27 Universal Usability (cont.) Screen-brightness preferences vary substantially knob to enable user control account for variances of user population's sense perception I VP R 53 Vision depth contrast color blindness motion sensitivity I VP R 54

28 Touch keyboard and touchscreen sensitivity I VP R 55 Hearing audio clues must be distinct I VP R 56

29 workplace design help and hinder work performance I VP R 57 Universal Usability (cont.) I VP R 58

30 draft standard Human Factors Engineering of Computer Workstations (2002) lists these concerns: Work-surface and display-support height Clearance under work surface for legs Work-surface width and depth Adjustability of heights & angles for chairs & work surfaces Posture seating depth and angle; back-rest height and lumbar support Availability of armrests, footrests, and palmrests I VP R 59 Universal Usability (cont.) I VP R 60

31 Cognitive and perceptual abilities Human ability to interpret sensory input rapidly initiate complex actions makes modern computer systems possible I VP R 61 Journal: Ergonomics Abstracts classification of human cognitive processes: Long-term and semantic memory Short-term and working memory Problem solving and reasoning Decision making and risk assessment Language communication and comprehension Search, imagery, and sensory memory Learning, skill development, knowledge acquisition and concept attainment I VP R 62

32 Universal Usability (cont.) I VP R 63 also factors affecting perceptual and motor performance Arousal and vigilance Fatigue and sleep deprivation Perceptual (mental) load Knowledge of results and feedback Monotony and boredom Sensory deprivation Nutrition and diet Fear, anxiety, mood, and emotion Drugs, smoking, and alcohol Physiological rhythms I VP R 64

33 But note, in any application background experience knowledge in task domain interface domain play key roles in learning and performance I VP R 65 Universal Usability (cont.) I VP R 66

34 Personality differences no set taxonomy for identifying user personality types designers must be aware: populations subdivided various responses to different stimuli I VP R 67 Myers-Briggs Type Indicator (MBTI) extroversion versus introversion sensing versus intuition perceptive versus judging feeling versus thinking I VP R 68

35 Universal Usability (cont.) I VP R 69 Cultural and international diversity Characters, numerals, special characters, and diacriticals Left-to-right versus right-to-left versus vertical input and reading Date and time formats Numeric and currency formats Weights and measures Telephone numbers and addresses I VP R 70

36 Names and titles (Mr., Ms., Mme.) Social-security, national identification, and passport numbers Capitalization and punctuation Sorting sequences Icons, buttons, colors Pluralization, grammar, spelling Etiquette, policies, tone, formality, metaphors I VP R 71 Universal Usability (cont.) I VP R 72

37 Users with disabilities plan early to accommodate users with disabilities more cost efficient than adding on later businesses must comply with "Americans With Disabilities" Act for some applications I VP R 73 Elderly Users Including elderly fairly easy allow for variability within applications settings for sound color brightness font sizes etc. I VP R 74

38 Goals for our profession Potential research topics Reduce anxiety and fear of computer usage Graceful Evolution Specification and implementation of interaction Direct manipulation Input devices Online assistance Information exploration I VP R 75 Goals for our profession (cont.) Provide tools, techniques, and knowledge for system implementers Rapid prototyping easy when using contemporary tools Use general or self-determined guideline documents written for specific audiences To refine systems, use feedback from individual or groups of users I VP R 76

39 Goals for our profession (cont.) Raise computer consciousness of general public Many novice users fearful due to experience with poor product design Good designs help novices through these fears by being clear competent nonthreatening I VP R 77