1 Usability analysis and inspection Why and how? Informationsteknologi Institutionen för informationsteknologi Why? n Iterative design n Prototyping n Measuring usability n Objective/subjective feedback n Quick and dirty n Slow and clean n With or without users Informationsteknologi Institutionen för informationsteknologi Evaluation Questions that might arise during systems development: n Will the switch board operator be able to answer more telephone calls per hour than before? n Will less customers have problems withdrawing cash from the ATM? n If a user enters a wrong number, what is the consequence and can we recover from it? Informationsteknologi Institutionen för informationsteknologi Evaluation n can we change the current menu structure without causing problems? n how fast can the users read text from the screen? n how long time will it take to find specific information n decreasing the font size from 12 p to 10 p, what consequences will it have? n how small can we make the buttons? Informationsteknologi Institutionen för informationsteknologi Evaluating usability n These questions are about usability n Usability can be measured through such questions n Evaluations typically address whether the system meets the requirements, it seldom explains the reasons behind the problems. Informationsteknologi Institutionen för informationsteknologi Measuring usability n No “silver bullet” n Evaluation during the development,not afterwards – usability is not only a measure but a goal for developers and development. n Usability builds on analysis and experiments. n Inexperienced developers often ignore validation in preference of verification of a system.
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Usability analysis andinspection
Why and how?
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Why?
n Iterative designn Prototypingn Measuring usabilityn Objective/subjective feedbackn Quick and dirtyn Slow and cleann With or without users
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EvaluationQuestions that might arise during systemsdevelopment:
n Will the switch board operator be able to answermore telephone calls per hour than before?
n Will less customers have problems withdrawingcash from the ATM?
n If a user enters a wrong number, what is theconsequence and can we recover from it? In
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Evaluationn can we change the current menu structure
without causing problems?n how fast can the users read text from the
screen?n how long time will it take to find specific
informationn decreasing the font size from 12 p to 10 p, what
consequences will it have?n how small can we make the buttons?
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Evaluating usability
n These questions are about usabilityn Usability can be measured through
such questionsn Evaluations typically address
whether the system meets therequirements, it seldom explains thereasons behind the problems.
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Measuring usabilityn No “silver bullet”n Evaluation during the development,not
afterwards – usability is not only a measure buta goal for developers and development.
n Usability builds on analysis and experiments.n Inexperienced developers often ignore validation
in preference of verification of a system.
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Costs for correcting errorsCosts
Time sinceprojectstart
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Analytical evaluationn A logical simulation of user behaviourn E.g. GOMS, KLM, Cognitive Walkthroughn Can be used to test things before they have
been built.n Saves time since we do not need to construct in
advance.n No user experiments necessary.n Create a sequence of steps and measure the
time per step.
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Empirical evaluation
n Let users try out a prototype
n Simple and cheap tests.
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Performance measurement
n Test users perform predefined tasksn Define a set of usability goalsn Measure errors and timesn Laboratory
+ Results in hard numbers, easy tocompare+ Objective results- time consuming, expensive- skilled users for skilled performance
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GOMS
Measuring speed of performanceDescribes different possible ways(sequences) of solving a problem
n Goal - a certain objective to be achievedn Operator - available actionsn Methods - Sequences of operatorsn Selection rules - when choosing between
methods
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GOMS modelGOAL: PHOTOCOPY PAPER
GOAL: LOCATE-ARTICLEGOAL: PHOTOCOPY-PAGE repeat until no more pages
n e.g. press key - 0.08 s, point withmouse - 1.10 s+ compare different methods- only on smaller parts of the work
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KLM modelOperation Anmärkning Tid (i sekunder)K Tryck ned tangent
Good maskinskrivare (90 ord/min.)Medelmåttig maskinskrivare (40 ord/min.)Icke-maskinskrivare
0,120,281,20
B Musknappstryckningner eller uppdubbelklick
0,100,20
P Peka med musenFitts lagMedelrörelse
0,1log(D/S+0,5)1,10
H Hand till eller från tangentbord 0,40D Rita (domänberoende) -M Mentalt förbereda sig 1,35R Respons från systemet -Tabell X: tider för vissa operationer som en operatör utför enligt KLM-metoden (efter Card,Moran & Newell, 1983)
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KLM examplen Exempel. Det finns två olika sätt att utföra
kommandot ”Spara”. Antingen kan man välja Ctrl-Ssom en tangentkombination på tangentbordet, ellerockså kan man välja alternativet spara i arkivmenyn.
n Alternativ 1: Ctrl S – T1= M + H + K = 1,35 + 0,40+ 0,28 = 2,03 sek
n Alternativ 2: Menyalternativ – T2= M + H + P + B +P + B = 1,35 + 0,40 + 1,10 + 0,10 + 1,10 + 0,10 =4,15 sek
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Thinking aloud
n users verbalise their thoughtsn identify misconceptions of the
system+ direct feedback from the users- not natural to think out loud- difficult to verbalise their decisions
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Questionnaires
n Subjective satisfaction+ Can be distributed to many people- Users answer what they think theydo, not what they actually do
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Cognitive Walkthrough
n An evaluator walks through the interfacen Tries to act as a usern Actions based on knowledge about users
+ Quick- Dirty- Does not involve users, difficult tocapture domain specific problems
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Cognitive walkthroughExplanatory learningn Constructed for novice usersn Suitable for walk-up-and-use-interfacesn A successive walkthrough of tasks based
on questions on different levelsß Does the user see the search alternative?ß Do the user select the right alternative?ß Do the user understand the system response?
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Card Sortingn Physical paper cards with text and imagesn The test person sorts the cards according
to importancen Good for sorting icons, concepts etc.n Can promote understanding and
relevance of concepts by usersn Requires real users for good results
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Heuristic evaluation
n Uses sets of guidelinesn Inspection of the interfacen Document potential usability
problems+ Easy to apply+ possible to use early in the design- Domain problems
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Heuristic evaluationn Jacob Nielsen, www.useit.comn Measures usabilityn Informal walkthroughn Cheap and simplen No users required, can be performed individually,
requires minimal planning, can be used early inthe process
n Concentrates on identifying errors in the design(good and bad)
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Heuristic evaluation method
n A group of evaluators (moreevaluators find more errors)
n 3-5 personsn Design heuristics help in the
inspection
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Heuristic evaluation
1. Simple and natural dialogue2. Speak the users language3. Minimise Users Memory Load4. Consistency5. Feedback6. Clearly marked exits7. Shortcuts8. Good error messages9. Prevent errors10. Help and documentation
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Simple and Natural dialogue
n Obvious how to interact with thesystem
n Grouping of objectsn Enough information on the screenn Overview and detailsn Avoid confusing decoration In
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Speak the users language
n Domain languagen Avoid system or computer languagen Use metaphors familiar to the usersn Icons, pictures, etc., relevant for the
domain
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Minimise user memory load
n Enough information on the screenn Recognition instead of recalln Highlight important informationn Show status informationn Default values
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Consistency
n Consistent layoutn Consistent interactionn Consistent languagen Consistent functionality
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Feedback
n Show waiting timesn Feedback for actionsn Work related feedbackn System failure
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Clearly marked exits
n Show the way the user has “walked”through the system
n How to get back and forwardn Oriented in the information space
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Shortcuts
n Use shortcuts to perform actionsn Type aheadn Jumps to a desired locationn Reuse of interaction history
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Good error messages
n Avoid obscure data coden “An error No 13 has occurred”n Use the users language
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Prevent error
n Dialogues for actions that may leadto serious consequences
n Avoid modesn Show statusn Support “undo” and “redo”
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Help and documentation
n Manuals should not be necessaryn Give on-line help on the users
initiativen If no other solution is possible, give
help at the initiative of the system
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Nielsen’s new designheuristics
n Visibility of system statusThe system should always keep users informed aboutwhat is going on, through appropriate feedback withinreasonable time.
n Match between system and the real worldThe system should speak the users’ language, withwords, phrases and concepts familiar to the user ratherthan system-oriented terms. Follow real-worldconventions, making information appear in a naturaland logic order
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Nielsen’s new designheuristics
n User control and freedomUsers often choose system functions bymistake and will need a clearly marked“emergency exit” to leave the unwanted statewithout having to go through an extendeddialogue. Support undo and redo.
n Consistency and standardsUsers should not have to wonder whetherdifferent words, situations, or actions meanthe same thing. Follow platform conventions.
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Nielsen’s new designheuristics
n Error preventionEven better than good error messages is a carefuldesign which prevents a problem from occurring inthe first place.
n Recognition rather than recallMake objects, actions and options visible. The usershould not have to remember information from onepart of the dialogue to another. Instructions for useof the system should be visible or easily retrievablewhenever appropriate.
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Nielsen’s new designheuristics
n Flexibility and efficiency of useAccelerators – unseen by the novice user – mayoften speed up the interaction for the expert usersuch that the system can cater to both inexperiencedand experienced users. Allow users to tailor frequentactions.
n Aesthetic and minimalist designDialogues should not contain information which isirrelevant or rarely needed. Every extra unit ofinformation in a dialogue competes with the relevantunits of information and diminishes their relativevisibility.
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Nielsen’s new designheuristicsn Help users recognise, diagnose and
recover from errorsError messages should be expressed in plainlanguage (no codes), precisely indicate the problem,and constructively suggest a solution.
n Help and documentationEven though it is better if the system can be usedwithout documentation, it may be necessary toprovide help and documentation. Any suchinformation should be easy to search, focused onthe user’s task, list concrete steps to be carried out,and not be too large.
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Heuristic evaluationn Not suitable for repeated analysis (with
the same person). Can be solved byrotating the inspection tasks
n Good results if the evaluators are skilledn Good in combination with real user
testing (the techniques complement oneanother)
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Grading the errors0 I do not agree that this is a usability problem at
all1 Cosmetic problem only2 Minor usability problem: should be given low
priority3 Major usability problem: important to fix, so
should be given high priority4 Usability catastrophe: imperative to fix this
before product can be released
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How to use the results
n Analyse the resultsn Identify solutions to the problemsn Create a new prototypen Optimising between requirements
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Formative evaluations
n Helps forming the systemn Iterative testing
n Summative evaluation – tests theentire system in the end (when it istoo late to do anything) In
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Formative evaluationsn Experience teaches you to build prototypes and
to make concrete decisionsn Informal user tests with simple prototypes
measures errors early and simple.n Field tests with prototypes with a series of
changes to measure difference in preference,error rate, speed, etc.
n Controlled experiments (all importantparameters are under control)
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Evaluation stepsn Identify usability aspects, specify special
requirements on the productn Produce a prototypen Prepare experiments (Find users, select
parameters to test, documentation method)n Test and collect datan Analysisn Conclusions In
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Evaluate...
Which method should you use and why?n Micro wave oven - which is the fastest
way of heating your food, 1.10 or1.11?
n System for phoning via your computer.n Public service phone (e.g. Bank, RSV)n Web site for finding courses (e.g.
