User interface design A software engineering perspective Soren Lauesen Slides for Chapter 1 November 2004 © 2005, Pearson Education retains the copyright to the slides, but allows restricted copying for teaching purposes only. It is a condition that the source and copyright notice is preserved on all the material.

User Interface Design2 Outline What is a user interface? Usability motivations Usability factors Usability problems Basics of usability testing Usability measurements and requirements

User Interface Design3 User Interface The part of the system that you see, hear and feel. Interactive computer systems –You initiate some action and system responds with some output –System prompts you to do something, and you have to respond with more inputs These interactions take place through the user interface.

User Interface Design4 Outline What is a user interface? Usability motivations Usability factors Usability problems Basics of usability testing Usability measurements and requirements

User Interface Design5 Design of user interfaces In principle, it is easy to make a user interface. –Just make it possible for the user to see and change all the data in the system. But it is not easy to make a user interface that is easy to use. –Ease of use is hard to define. –Ease of use is hard to evaluate.

User Interface Design6 All factors important. Hard to measure, but possible. Fig 1.1B Quality factors Easy to make a user interface: Just give access to the database Hard to make a good user interface Quality factors: Correctness Availability Performance Security Ease of use Maintainability... Functionality: Necessary features see, edit create, delete Database

User Interface Design7 Usability motivations Many interfaces are poorly designed and this is true across domains: Life-critical systems –Air traffic control, nuclear reactors, power utilities, police & fire dispatch systems –High costs, reliability and effectiveness are expected –Length training periods are acceptable despite the financial cost to provide error-free performance and avoid the low frequency but high cost errors –Subject satisfaction is less an issue due to well motivated users From Shneiderman, Ch. 1

User Interface Design8 Usability motivations (cont.) Industrial and commercial uses –Banking, insurance, order entry, inventory management, reservation, billing, and point-of- sales systems –Ease of learning is important to reduce training costs –Speed and error rates are relative to cost –Speed of performance is important because of the number of transactions –Subjective satisfaction is fairly important to limit operator burnout

User Interface Design9 Usability motivations (cont.) Office, home, and entertainment applications –Word processing, electronic mail, computer conferencing, and video game systems, educational packages, search engines, mobile device, etc. –Ease of learning, low error rates, and subjective satisfaction are paramount due to use is often discretionary and competition fierce –Infrequent use of some applications means interfaces must be intuitive and easy to use online help is important –Choosing functionality is difficult because the population has a wide range of both novice and expert users –Competition cause the need for low cost

User Interface Design10 Usability motivations (cont.) Exploratory, creative, and cooperative systems –Web browsing, search engines, artist toolkits, architectural design, software development, music composition, and scientific modeling systems –Collaborative work –Benchmarks are hard to describe for exploratory tasks and device users –With these applications, the computer should "vanish" so that the user can be absorbed in their task domain

User Interface Design11 Usability motivations (cont.) Social-technical systems –Complex systems that involve many people over long time periods –Voting, health support, identity verification, crime reporting –Trust, privacy, responsibility, and security are issues –Verifiable sources and status feedback are important –Ease of learning for novices and feedback to build trust –Administrators need tools to detect unusual patterns of usage

User Interface Design12 Outline What is a user interface? Usability motivations Usability factors Usability problems Basics of usability testing Usability measurements and requirements

User Interface Design13 Usability factors Fit for use – the system supports the processes and tasks that the user needs to perform. Ease of learning – the system is easy to learn for various groups of users. Task efficiency – frequent users can perform their tasks efficiently. Ease of remembering – occasional users find it easy to remember what to do. Subjective satisfaction - how satisfied is the user? Understandability – it is easy to understand the system’s behavior, especially in error cases.

User Interface Design14 Outline What is a user interface? Usability motivations Usability factors Usability problems Basics of usability testing Usability measurements and requirements

User Interface Design15 Usability problems Anything about the application that hampers a user in performing his task. Usability problems are a special kind of software defect. The system works as intended by the developer, yet the user finds it hard to get useful work out of the system.

User Interface Design16 Examples: The system works as intended by the programmer, but the user: P1.Cannot figure out how to start the search. Finally finds out to use F10. P2. Believes he has completed the task, but forgot to push Update. P3. Sees the discount code field, but cannot figure out which code to use. P4. Says it is crazy to use six screens to fill in ten fields. P5.Wants to print a list of discount codes, but the system cannot do it. Fig 1.3 Usability problems Severity classes: 1Missing functionality 2Task failure 3Annoying 4Medium problem (succeeds after long time) 5Minor problem (succeeds after short time) Critical problem = Missing functionality, task failure, or annoying

User Interface Design17 Severity classes Missing functionality – the system cannot support the user’s task. Task failure – the user fails (knowingly or unknowingly) to complete the task on his own. Annoying – the user complains that the system is cumbersome. Medium – the user succeeds after stumbling around for a long time. Minor – the user succeeds after a few attempts.

User Interface Design18 Outline What is a user interface? Usability motivations Usability factors Usability problems Basics of usability testing Usability measurements and requirements

User Interface Design19 Usability testing One variant –Method: think-aloud test –System under test: Real system – carry out various tasks Prototype – evaluate window contents and navigation –Team Facilitator – talks with the user Log keeper – records the test session Observer – extra

User Interface Design20 Purpose: Find usability problems Fig 1.4 Usability test - think aloud User Performs tasks Thinks aloud Logkeeper Listens Records problems Facilitator Listens Asks as needed I try this because... User doesn’t notice...

User Interface Design21 Prototypes A primitive version of a system. Uses: –Demonstrate technical feasibility. Develop only the necessary technical portions. –Check performance early in development. Develop the performance-critical portions and simulate heavy load. –Basis for discussion with stakeholders. Develop main screens. (“Demo” versions.)  Test usability of system. Develop user interface portion.

User Interface Design22 Kinds of prototypes Paper prototypes –Hand-drawn mock-up –Tool-drawn mock-up Computer-based –Screen prototype –Functional prototype

User Interface Design23 Purpose: Find usability problems Usability specialist looks at system using common sense and/or guidelines The specialist lists problems (Consults with other experts) Fig 1.5 Heuristic evaluation First law of usability: Heuristic evaluation has only 50% hitrate Actual problems Predicted problems False problems Missed problems Expert - reviewer

User Interface Design24 Heuristic evaluation Engage a usability specialist as consultant. Potentially more convenient that arranging for usability tests with real users. Usability expert has lots of experience with user interfaces but often lacks the domain knowledge for the application. May lead to a lot of false positives. –Usability specialist may point out problems that don’t really cause problems to real users. –Fixing these may be a waste of developers’ time. –Fixing these may actually make the system worse. May fail to uncover serious usability problems arising from missing functionalities or complex scenarios.

User Interface Design25 User review Engage a domain expert as usability consultant and walk him through the scenarios. Domain expert can point out missing functionalities and imagine complex tasks that might be difficult to accomplish with your user interface. However, experts often miss the trivial things that trip the novice user.

User Interface Design26 Outline What is a user interface? Usability motivations Usability factors Usability problems Basics of usability testing Usability measurements and requirements

User Interface Design27 Usability measures Task time – time it takes the user to complete the given task. Problem counts – number of usability problems uncovered. Keystroke counts – how many keystrokes, mouse clicks and other operations did the user employ in order to complete the task? Opinion poll – user completes a questionnaire after usability testing. Score for understanding – quiz the user about the system’s behavior. Guidelline adherence – identify deviations from interface standards and guidelines.

User Interface Design28 ATM Users:20 bank customers, random selection. Task 1:Withdraw $100 from ATM. No instructions. Measure:How many succeed in 2 min? Task 2:Withdraw as much as possible ($174) Measure:How many succeed in 5 min? Reqs:Task 1: 18 succeed. Task 2: 12 succeed. How to measure What to measure Requirement - target Fig 1.6A Measuring usability - task time (performance) Pros:Classic approach. Good when buying. Cons:Not good for development. Not possible early. Little feedback. Internal ordering system Users:5 secretaries in the company. Have tried the internal ordering system. Have not used it for a month. Task 1:Order two boxes of letter paper +... Measure:Average time per user. Reqs:Average time below 5 min. What to measure Risky!

User Interface Design29 Users:20 bank customers... Measure:In 2 min? Reqs:Task 1: 18 succeed. Task 2: 12 succeed. Fig 1.6B Choosing the numbers Why 20? Cost versus reliability. During development: One, later two, later... Why 2 mins? Best practice, ideal way... Why 18? 90% of customers should succeed. Task 2 harder. Open target Reqs:18 out of 20 must succeed within ____ min. We expect around 2 min. Specify how, what, and expectations. Wait and see what is possible.

User Interface Design30 Users:3 potential users. Think-aloud test. Record usability problems. Task 1:Order two boxes of letter paper +... Task 2:... Measure:Number of critical problems per user. Number of medium problems on list. Reqs:Max one user encounters critical problems. Max 5 medium problems on the list. What to measure Requirement Fig 1.6C Measuring usability - Problem counts Pros:Possible early - mockup sufficient. Good feedback to developers. Cons:Best for ease of learning. Only indications for other factors. How to measure

User Interface Design31 Task 1:Withdraw a standard amount from ATM. Task 2:... Measure:Number of keystrokes and mouse clicks. Reqs:Max keystrokes 6 - incl. PIN code. Total system response time max 8 s. How to measure What to measure Requirement Fig 1.6D Measuring usability - Keystroke counts Pros:No users needed. Possible early - mockup sufficient. Cons:Not sure users find the fast way. Only task efficiency. Total task time s3.6 s total system response time 8.0 s Total task time11.6 s Plus other user actions?

User Interface Design32 Ask 20 novice users to complete the questionnaire. Measure:Count number of entries per box. Reqs:80% find system easy to learn. 50% will recommend it to others. How to measure What to measure Requirement Fig 1.6E Measuring usability - Opinion poll Pros:Widely used. You may ask for any usability factor. Cons:Doesn’t match objective evidence. Only indications during development. Little feedback to developers. Questionnaire agreeneutraldisagree The system was easy to learn The system is easy to use The system helps me... It is fun to use I will recommend it to others

User Interface Design33 Ask 5 potential ATM users what these error messages mean: Amount too large PIN code invalid... Ask them also: What would the system do if... Measure:Assess answers on scale A-D. Reqs:80% of answers marked A or B. How to measure What to measure Requirement Fig 1.6F Measuring usability - Score for understanding Pros:Easy way to test understandability. Best way to cover error messages. Useful both early and late in development. Cons:Only measures understandability..

User Interface Design34 Ask an expert to review the user interface and identify deviations from guideline X. (Or ask two experts to come up with a joint list.) Measure:Number of deviations per screen. Reqs:At most one deviation per screen. How to measure What to measure Requirement Fig 1.6G Measuring usability - Guideline adherence Pros:Adherence helps users switch between systems. Company-specific guidelines for internal systems can help even more. Cons:Cannot guarantee high usability. Developers find guidelines hard to follow - examples help best.

User Interface Design35 Fig 1.6H Which usability measure? Task time Problem counts Keystroke counts Opinion poll Score for underst. Guidelines Fit for use Ease of learning Task efficiency Ease of remember Subjective satisf. Understandability ?? Highly useful Some use Indications only Development, early Development, late Buying a system

Usability Testing Exercise March 6, :30-8:30 PKI 269

User Interface Design37 Objectives Participate in and experience an actual usability testing session. Get a feel for how the Linked View Data Visualization requirements were interpreted and implemented by different students.

User Interface Design38 Usability test It is the system being tested, not you. One-on-one between developer and user. Developer is also facilitator/observer. You will be asked to perform a set of tasks. Remember to think aloud as you perform the tasks. –Explain what you are up to and why. –This is your primary responsibility. Other things can be pointed out too –Point out anything that might be hard to understand or inconvenient to use. –Point out style issues (color, placement of buttons) if they hinder your understandability. –Be constructive (“I find it hard to read this” rather than “I don’t like the way this was implemented”)

User Interface Design39 Usability test (con’t) Expect some crashes, some of these systems are not quite finished. Each testing period is 30 minutes long, but do not panic if you are running out of time –Remember: it’s the system being tested, not you. Short debriefing (Q&A) with developer after each session.

User Interface Design40 Cars data make - Make of car model - Model of car mpg - Miles/(US) gallon cyl - Number of cylinders disp - Displacement (cu.in.) hp - Gross horsepower drat - Rear axle ratio wt - Weight (lb/1000) qsec - 1/4 mile time vs - V/S (???) am - Transmission (0 = automatic, 1 = manual) gear - Number of forward gears carb - Number of carburetors

User Interface Design41 Usability data UserNo - ID for a particular user TaskNo - Task # executed by user Comp - 1 = user completed the task, 0 = user did not complete the task DurInMin - How long (in minutes) it took to complete the task DurInSec - DurInMin * 60 UProbs - number of usability problems recorded Sev1 - number of severity 1 problems recorded (most severe) Sev2 - number of Severity 2 problems recorded Sev3 - number of Severity 3 problems recorded Sev4 - number of Severity 4 problems recorded Sev5 - number of Severity 5 problems recorded (least severe) NoSev - 1 = observer did not record severity, 0 = observer recorded severity

User Interface Design42 A demo Paper prototype (If time permits) Ggobi system Task: –Use the system and answer the question, “Is there a relationship between horsepower and weight?” –Use the system and answer the question, “For cars with 6 cylinders, is there a relationship between horsepower and the quarter-mile time?"