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User Interface Design Southern Methodist University CSE 8316 Spring 2003 Temporal Relations and Usability Specifications Introduction • Previous chapter discussed low level primitives • Now focus on abstraction and relative timing of events • Such issues as interruptibility and interleavability should be part of interaction design and not driven by constructional design. Introduction • UAN can be used to specify: – Sequence – Iteration – Optionality – Repeating choice – Order independence – Interruptibility – Interleavability – Concurrency – Waiting Sequencing and Grouping • Sequence – Sequence: One task is performed in its entirety before the next task is begun – Represent in the UAN by grouping (horizontally or vertically) without any intervening operators • Grouping – Tasks can be grouped together using various operators to form new tasks – Definition is similar to that for regular expressions Abstraction • Have only seen UAN describing articulatory actions -- primitive tasks performed by the user. • In this form, describing an entire interaction design would be overly complex and difficult • Introduce abstraction by allowing groups of tasks to be named. • As with procedures, a reference to the name is equivalent to performing all the tasks described by that name Abstraction • To aid in reusability, allow tasks references to be parameterized • Reusing tasks promotes logical decomposition, providing for consistent system model • Abstraction hides details, but also hides user feedback. This information can be listed at one or both levels. • With task naming, can now perform top- down design. Task Operators • Choice – Simple choice is represented in UAN with the vertical bar, `|'. – Repeating choice is formed by adding the iterators `*' and `+'. Task Operators • Order Independence – Set of tasks that must be completed before continuing, but order of completion of the subtasks is not important. – Represented by the `&'. Task Operators • Interruption – Interruption occurs when one task is suspended while another task is started – Since UAN describes what can happen, you cannot specify an interruption, but rather what can be interrupted (interruptibility) – To specify that A can interrupt B use A - -> B. Task Operators • Uninterruptible Tasks – Assume all primitive actions are uninterruptible (e.g. pressing a mouse button). – Specify the uninterruptibilty of higher- level tasks (e.g. modality) by enclosing in brackets, `<A>'. Task Operators • Interleavability – If two tasks can interrupt each other, they are considered interleavable. – Assume that operator is transitive. – Represented with double arrow, A <--> B. Task Operators • Concurrency – If two tasks can be performed in parallel (e.g. two different users), then tasks are concurrent Represented with `||'. Task Operators • Intervals and Waiting – Can add explicit time intervals between two events. – Two forms: • If task B must be completed within n seconds of task A: `A (t<n) B' • If task B is to occur only n seconds after task A: `A (t>n) B' Other Representations • Screen Pictures and Scenarios – UAN describes user actions, but does not describe the format/display of screens – Should supplement UAN with screen layouts and scenarios. • State Transition Diagrams – Typical interface contains various states – To provided global view of how states are related, add state transition diagram to UAN Design Rationale • Basic role of UAN is communication • Important to provide reasons behind various decisions • Gives motivation and goals and helps prevent later duplication of mistakes Usability Specifications Usability Specifications • Quantitative, measurable goals for knowing when the interface is good enough • Often overlooked, but provide insurance that multiple iterations are converging • For this reason, should be established early Usability Specification Table • Convenient method for indicating parameters • Contains following information – Usability Attribute – Measuring Instrument – Value to be Measured – Current Level – Worst Acceptable Level – Planned Target Level – Best Possible Level – Observed Results Usability Attribute • Represents the usability characteristic being measured • Must determine classes of intended users • For each class determine realistic set of tasks • Goal is to determine what user performance will be acceptable Usability Attributes • Typical attributes include: – Initial Performance: User's performance during the first few uses. – Long-term Performance: User's performance after extended use of the product – Learnability: How quickly the user learns the system – Retainability: How quickly does the knowledge of how to use the system dissipate Usability Attributes – Advanced Feature Usage: Usability of sophisticated features – First Impression: Subjective user feelings at first glance – Long-term User Satisfaction: User's opinion after extended use Measuring Instrument • Method to find a value for a usability attribute • Quantitative, but may be objective or subjective • Objective: based on user task performance • Subjective: deal with user opinion (questionnaires) • Both types are needed to effectively evaluate Benchmark Tasks • User is asked to perform a task using the interface • Most common objective measure • Task should be a specific, single interface feature • Description should be clearly worded without describing how to do it Questionnaire • Quantitative measure for subjective feelings • Creating survey that provides useful data is not trivial • Recommend use of scientifically created question (e.g. QUIS) Values To Be Measured • The data value metric • Typically metrics are: – Time for task completion – Number of errors – Average scores/ratings on questionnaire – Percentage of task completed in a given time – Ratio of successes to failures – Time spent in errors and recovery Values To Be Measured – Number of commands/actions used to perform task – Frequency of help/documentation use – Number of repetitions of failed commands – Number of available commands not invoked – Number of times user expresses frustration or satisfaction Setting Levels • Having determined what and how to measured, need to set acceptable levels • These levels will be used to determine when the interface has reached the appropriate level of usability • Important to be specific enough so that levels can be reasonably set Current Level • Present level of the value to be measured • Values can be determined from manual system, current automated system or prototypes • Proof that usability attribute can be measured • Baseline against which new system will be judged Worst Acceptable Level • Lowest acceptable level of user performance • This level must be attained for the product to be considered complete • Not a prediction of how the user will perform, but rather the worst performance that is considered acceptable Worst Acceptable Level • Tendency/pressure is to set the values too low • Good rule of thumb is to set them at or near the current levels Planned Target Level • The level of unquestioned usability, the ideal situation • Serve to focus attention on those aspects needing the most work (now or later) • May be based on competitive systems Best Possible Level • State-of-the-art upper limit • Provides goals for next versions • Gives indication of improvement that is possible • Frequently determined by having measuring expert user Observed Results • Actual values obtained from user testing • Provides quick comparison with projected levels Setting Levels • There are various methods for estimating the levels: – Existing systems or previous versions of new system – Competitive systems – Performing task manually – Developer performing with prototype – Marketing input based on observations of user performance on existing systems Setting Levels • The context of the task is important in determining these levels Example usability table Usability Measuring Value to be Current Worst Planned Best Observed attribute instrument measured level accepta target possible results ble level level level Advanced “Add Length of 13 minutes 2 1 minute 30 feature repeating time to add a (manually) minutes seconds usage appointment weekly ” task per appointment benchmark 3 every week for one year after one hour of use Example usability table Usability Measuring Value to be Current Worst Planned Best Observed attribute instrument measured level accepta target possible results ble level level level First User Number of ?? 10 5 2 impression reaction negative/posi negative negative/ negative tive remarks /2 5 /10 during the positive positive positive session Example usability table Usability Measuring Value to be Current Worst Planned Best Observed attribute instrument measured level accepta target possible results ble level level level Learnability “Add Length of 15 15 12 8 appointme time to seconds seconds seconds seconds nt” task successfully (manually) per add benchmark appointment 5 after one hour of use Cautions • Each usability attribute should be (realistically) measurable • User classes need to be clearly specified • The number of attributes to be measured should be reasonable. Start small and add as experience grows • All project members should agree on the values Cautions • The values should be reasonable – If found to be too low, then increase them on next iteration – If they appear too high, it may be they were not realistically set or that the interface needs a lot of work! Judgement call Expert Reviews, Usability Testing, Surveys, and Continuing Assessment Introduction • Designers can become so entranced with their creations that they may fail to evaluate them adequately • Experienced designers have attained the wisdom and humility to know that extensive testing is a necessity Introduction • The determinants of the evaluation plan include: – stage of design (early, middle, late) – novelty of project (well defined vs. exploratory) – number of expected users – criticality of the interface (life-critical medical system vs. museum exhibit support) Introduction – costs of product and finances allocated for testing – time available – experience of the design and evaluation team Introduction • The range of evaluation plans might be from an ambitious two-year test to a few days test. • The range of costs might be from 10% of a project down to 1%. Expert Reviews • While informal demos to colleagues or customers can provide some useful feedback, more formal expert reviews have proven to be effective. • Expert reviews entail one-half day to one week effort, although a lengthy training period may sometimes be required to explain the task domain or operational procedures. Expert Reviews • There are a variety of expert review methods to chose from: – Heuristic evaluation – Guidelines review – Consistency inspection – Cognitive walkthrough – Formal usability inspection Expert Reviews • Expert reviews can be scheduled at several points in the development process when experts are available and when the design team is ready for feedback. • Different experts tend to find different problems in an interface, so 3-5 expert reviewers can be highly productive, as can complementary usability testing. Expert Reviews • The dangers with expert reviews are that the experts may not have an adequate understanding of the task domain or user communities. Expert Reviews • To strengthen the possibility of successful expert reviews it helps to chose knowledgeable experts who are familiar with the project situation and who have a longer term relationship with the organization. • Moreover, even experienced expert reviewers have great difficulty knowing how typical users, especially first-time users will really behave. Usability Testing and Laboratories • The emergence of usability testing and laboratories since the early 1980s is an indicator of the profound shift in attention to user needs. • The remarkable surprise was that usability testing not only sped up many projects but that it produced dramatic cost savings. Usability Testing and Laboratories • The movement towards usability testing stimulated the construction of usability laboratories. Usability Testing and Laboratories • A typical modest usability lab would have two 10 by 10 foot areas, one for the participants to do their work and another, separated by a half-silvered mirror, for the testers and observers (designers, managers, and customers). Usability Lab (Interface Analysis Associates) Usability Lab (Interface Analysis Associates) Usability Testing and Laboratories • Participants should be chosen to represent the intended user communities, with attention to background in computing, experience with the task, motivation, education, and ability with the natural language used in the interface. Usability Testing and Laboratories • Participation should always be voluntary, and informed consent should be obtained. Professional practice is to ask all subjects to read and sign a statement like this one: – I have freely volunteered to participate in this experiment. – I have been informed in advance what my task(s) will be and what procedures will be followed. Usability Testing and Laboratories – I have been given the opportunity to ask questions, and have had my questions answered to my satisfaction. – I am aware that I have the right to withdraw consent and to discontinue participation at any time, without prejudice to my future treatment. – My signature below may be taken as affirmation of all the above statements; it was given prior to my participation in this study. Usability Testing and Laboratories • Videotaping participants performing tasks is often valuable for later review and for showing designers or managers the problems that users encounter. • Field tests attempt to put new interfaces to work in realistic environments for a fixed trial period Nomos Lab An observer's view of a test being carried out in the purposely designed Nomos lab. Nomos Lab Two sides of the one-way glass - actions and problems are logged while the user carrys out real tasks with the product. Usability Testing and Laboratories • Field tests can be made more fruitful if logging software is used to capture error, command, and help frequencies plus productivity measures Usability Testing and Laboratories • Game designers pioneered the can-you- break-this approach to usability testing – providing energetic teenagers with the challenge of trying to beat new games • This is a destructive testing approach – users try to find fatal flaws in the system, or otherwise to destroy it – has been used in other projects and should be considered seriously Usability Testing and Laboratories • Usability testing does have at least two serious limitations – it emphasizes first-time usage – has limited coverage of the interface features. • These and other concerns have led design teams to supplement usability testing with the varied forms of expert reviews. Siemens Usability Lab A control deck (shown above) allows the team to witness users reacting to software as they navigate the interface and attempt to perform normal tasks. Separate cameras record facial expressions and comments, use of manuals, and activity on the screen itself. As a rule, every session is recorded and held for later review and analysis. Siemens Usability Lab This section of the Siemens Center has been arranged so the software design team can view every move the user makes, interact with him or her when necessary, and generally see and feel their own design through the user's experience. Inventory of Facilities - U of Indiana • 2 Sony DXC-107A CCD Color Video Cameras, equipped with Canon R-II electrically controlled zoom lenses and wall-mounted on Pelco remote-control pan/tilt bases. All camera functions are remotely controlled from the observation room by Pelco MPTAZ Pan/Tilt and Scanner controls. • 2 Microphones: 1 Audio-Technical superhypercardioid (super shotgun) type for discrete data collection and a cardioid microphone for narration and overdubbing. • 1 Teac TASCAM M-06 six channel professional audio mixer, monitored via 5W self-amplified speakers or headphones. • 2 Scan converters: 1 Extron Super Emotia high resolution scan converter for capturing live video from the subject's computer screen, and 1 Mediator medium-resolution scan converter for titling and effects generation. • 2 Macintosh PowerMac 7500/100 workstations with 1710AV 17" monitors: 1 located in the testing room for use in evaluating Macintosh software, and 1 located in the observation room for data analysis, effects generation, and web-server functions. Both machines feature video capture and output (via scan converter) capabilities, and are networked onto both the local LAN (Novell ipx/spx) and Internet (TCP/IP). • 1 Dell XPS-90 Workstation with Dell 17" multiscanning monitor, located in the testing room for use in evaluating PC-compatible software. This machine is also networked onto both the local LAN (Novell ipx/spx) and Internet (TCP/IP). • 1 Sony PVM-411 video monitor rack for monitoring all online video sources. • 3 JVC BRS-800U industrial video cassette recorders, equipped with SA-R50U time code generator/reader boards and SA-K26U RS-422 interface boards: 2 for capturing camera output and 1 for capturing scan convertor (computer screen) output. Each can function independently or can be slaved to a single universal RMG-30U serial remote control. Inventory of Facilities - U of Indiana • 3 JVC TM-131SU Color Video Monitors located in the observation room for monitoring online sources during the evaluation session and providing high-quality output for post-session analysis and mixdown. • 1 JVC RMG-800U Editing Control Unit for post-production assemble/insert mixdown of recorded video source into condensed "highlights" tapes. • 1 Panasonic WAV7 Digital Effects Generator/Mixer for creating a variety of online and post- production video effects including wipes, fades, cuts, strobes, keys, mosaics, split-screen and picture-in-picture effects. • 1 Optimus SCT-53 "Pro Series" dual audio cassette deck with auto-reverse, dual digital time counters, and high speed dubbing capabilities. • Speakerphone equipped with a flashing silent ringer and a digital voicemail box. • Requisite cabling, stands, tables and other paraphernalia to allow above equipment to function and be used properly. Surveys • Written user surveys are a familiar, inexpensive and generally acceptable companion for usability tests and expert reviews. • The keys to successful surveys are clear goals in advance and then development of focused items that help attain the goals. Surveys • Survey goals can be tied to the components of the Objects and Action Interface model of interface design. Users could be asked for their subjective impressions about specific aspects of the interface such as the representation of: – task domain objects and actions – syntax of inputs and design of displays. Surveys • Other goals would be to ascertain – users background (age, gender, origins, education, income) – experience with computers (specific applications or software packages, length of time, depth of knowledge) – job responsibilities (decision-making influence, managerial roles, motivation) – personality style (introvert vs. extrovert, risk taking vs. risk aversive, early vs. late adopter, systematic vs. opportunistic) Surveys – reasons for not using an interface (inadequate services, too complex, too slow) – familiarity with features (printing, macros, shortcuts, tutorials) – their feeling state after using an interface (confused vs. clear, frustrated vs. in-control, bored vs. excited). Surveys • Online surveys avoid the cost of printing and the extra effort needed for distribution and collection of paper forms. • Many people prefer to answer a brief survey displayed on a screen, instead of filling in and returning a printed form, although there is a potential bias in the sample. Summary • Extensive testing is a necessity • Formal expert reviews have proven to be effective • Must have an adequate understanding of the task domain and user communities • Usability testing speeds up project TTM and produces dramatic cost savings Product Evaluations Evaluation During Active Use • A carefully designed and thoroughly tested system is a wonderful asset, but successful active use requires constant attention from dedicated managers, user- services personnel, and maintenance staff. • Perfection is not attainable, but percentage improvements are possible and are worth pursuing. Evaluation During Active Use Evaluation During Active Use • Interviews and focus group discussions – Interviews with individual users can be productive because the interviewer can pursue specific issues of concern. – After a series of individual discussions, group discussions are valuable to ascertain the universality of comments. Evaluation During Active Use • Continuous user-performance data logging – The software architecture should make it easy for system managers to collect data about the patterns of system usage, speed of user performance, rate of errors, or frequency of request for online assistance. – A major benefit of usage-frequency data is the guidance they provide to system maintainers in optimizing performance and reducing costs for all participants. Evaluation During Active Use • Online or telephone consultants – Online or telephone consultants are an extremely effective and personal way to provide assistance to users who are experiencing difficulties. – Many users feel reassured if they know there is a human being to whom they can turn when problems arise. Evaluation During Active Use – On some network systems, the consultants can monitor the user's computer and see the same displays that the user sees while maintaining telephone voice contact. – This service can be extremely reassuring; the users know that someone can walk them through the correct sequence of screens to complete their tasks. Evaluation During Active Use • Online suggestion box or trouble reporting – Electronic mail can be employed to allow users to send messages to the maintainers or designers. – Such an online suggestion box encourages some users to make productive comments, since writing a letter may be seen as requiring too much effort. Evaluation During Active Use • Online bulletin board or newsgroup – Many interface designers offer users an electronic bulletin board or newsgroups to permit posting of open messages and questions. – Bulletin-board software systems usually offer a list of item headlines, allowing users the opportunity to select items for display. – New items can be added by anyone, but usually someone monitors the bulletin board to ensure that offensive, useless, or repetitious items are removed. Evaluation During Active Use • User newsletters and conferences – Newsletters that provide information about novel interface facilities, suggestions for improved productivity, requests for assistance, case studies of successful applications, or stories about individual users can promote user satisfaction and greater knowledge. Evaluation During Active Use – Printed newsletters are more traditional and have the advantage that they can be carried away from the workstation. – Online newsletters are less expensive and more rapidly disseminated – Conferences allow workers to exchange experiences with colleagues, promote novel approaches, stimulate greater dedication, encourage higher productivity, and develop a deeper relationship of trust. Controlled Psychologically- oriented Experiments • Scientific and engineering progress is often stimulated by improved techniques for precise measurement. • Rapid progress in the designs of interfaces will be stimulated as researchers and practitioners evolve suitable human-performance measures and techniques. Controlled Psychologically- oriented Experiments • The outline of the scientific method as applied to human-computer interaction might comprise these tasks: – Deal with a practical problem and consider the theoretical framework – State a lucid and testable hypothesis – Identify a small number of independent variables that are to be manipulated – Carefully choose the dependent variables that will be measured Controlled Psychologically- oriented Experiments – Judiciously select subjects and carefully or randomly assign subjects to groups – Control for biasing factors (non-representative sample of subjects or selection of tasks, inconsistent testing procedures) – Apply statistical methods to data analysis – Resolve the practical problem, refine the theory, and give advice to future researchers Controlled Psychologically- oriented Experiments • Managers of actively used systems are coming to recognize the power of controlled experiments in fine tuning the human-computer interface. • Limited time, and then performance could be compared with the control group. Dependent measures could include performance times, user-subjective satisfaction, error rates, and user retention over time.
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