Usability EngineeringUsability Engineering

Dr. Dania BilalIS 582

Spring 2007

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Usability Engineering?Usability Engineering?

Measures multiple components of the user interface

Addresses the relationships between system and its users

Focuses on the HCI field

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What Is Usability Engineering?What Is Usability Engineering? Bridges the gap between human and

machines Measures the quality of a system in

relation to its intended users Involves several methods, each applied at

appropriate time of the design and development process

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Importance of UsabilityImportance of Usability

The sooner problems are found, the less expensive it is to fix them– Saves money by reducing designers’

timeProvides information about user

experience– Cognitive, affective, and psychomotor• Depends on method(s) employed

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Importance of UsabilityImportance of Usability

Learn more about users, tasks, expectations, successes, failures, information seeking, etc. and take these into consideration in redesigning a system or designing new one

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Usability AttributesUsability Attributes

As described by Neilsen– Learnability– Efficiency–Memorability– Errors & their severity– Subjective satisfaction

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LearnabilityLearnability

System must be easy to learn, especially for novice users– Hard to learn• systems are usually designed for expert

users– Learning curve for novice and expert

users

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EfficiencyEfficiency

System should be efficient to use so that once the user has learned how to use it, the user can achieve a high level of productivity– Efficiency increases with learning

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MemorabilityMemorability

System should be easy to remember, especially by casual users– No need to learn how to use system all

over again after a period of not using it

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Errors Errors

System should have a low error rateSystem should provide user with a

recovery mechanism–Minor errors–Major errors

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Minor ErrorsMinor Errors

Errors that did not greatly slow down user’s interaction with the system

User is able to recover from them– through system feedback– through awareness of error made

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Major ErrorsMajor Errors

Difficult to recover from themLead to faulty work if high in

frequencyMay not be discovered by the user– Errors can be catastrophic

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Subjective SatisfactionSubjective Satisfaction

System should be likeable by users (affective)

Satisfaction varies with purpose of system – Educational vs. entertainment

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AssumptionsAssumptions The designer’s best guess is not good enough The user is always right The user is not always right Users are not designers Designers are not users More features are not always better Minor interface details matter Online help does not really helpSource: Nielsen, J. (1993). Usability Engineering. San Diego: Morgan Kaufman.

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Factors Influencing User InteractionFactors Influencing User Interaction

Address the functionality of the system vis-à-vis:– user needs– user tasks– user information seeking – user expectations– user cognitive processes

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EvaluationEvaluation

Component of usability engineeringInvolves users in the evaluationUsers perform tasks developed by

evaluatorMain goal– Uncover problems and correct them

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EvaluationEvaluation

Can be done before, during, and after system is designed and developed– Before design– During design– After release

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Usability Methods: Cognitive Usability Methods: Cognitive WalkthroughWalkthrough Involves experts acting on behalf of actual

users Goal- and task- driven of how user

approaches a task in a system An observer “experimenter” is present– Prepares tasks– Takes notes– Provides help

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Usability TestingUsability Testing Actual users interact with system Users perform tasks assigned by

evaluator Users’ activities are captured– Methods

Users may also be interviewed Captured data are coded, analyzed, and

reported Interview data are coded, analyzed, and

reported

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Heuristic EvaluationHeuristic EvaluationEvaluators interact with an interface

several times and map interface to specific heuristics or guidelines– See Neilsen’s ten heuristics

Each evaluator generates a reportReports are aggregated and final

report is generatedAn observer may be present

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Field StudiesField StudiesActual usersUsers are observed in naturalistic

setting No tasks are assigned to usersUsers’ interaction with system are

captured, analyzed, interpreted, etc.Interviews can be used in addition to

observations

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Usability HeuristicsUsability Heuristics http://www.usabilityfirst.com/methods http://

www.useit.com/papers/heuristic/heuristic_list.html (Neilsen’s usability heuristics)

http://www.useit.com/papers/heuristic/heuristic_evaluation.html (how to conduct a heuristic evaluation)

http://www.uie.com/articles (collection of articles) http://www.uie.com/articles/usability_tests_learn/

Learning about usability test (Jared Spool) http://www.useit.com/papers/heuristic/severityrating.

html (Severity rating)

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Usability TestsUsability Tests

Stages– Preparation– Introduction– User interaction and caputre– Debriefing

Neilsen, J. (1993). Usability Engineering. San Diego: Morgan Kaufman.

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PreparationPreparation

Preparation for the experiment and data collection– Location of test (e.g., room to be used)– System to be used, capturing software,

etc.– Test materials, instructions,

questionnaires to be completed, as applicable

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IntroductionIntroduction

Purpose of the test– Results will be used to improve

interfaceUser cnfidentiality & IRBSoftware and equipment used to

collect data

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IntroductionIntroduction

Users to ask questions before and during experiment– Type of questions accepted

Users to report problems and difficulty in using system (e.g., screen freeze)

May provide verbal instructions

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Running the TestRunning the Test

Experimenter(s) should refrain from interacting with users– Don’t give your personal opinion– Don’t tell user how to perform certain

function– Don’t distract user during the

interaction

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DebriefingDebriefingUser is debriefed after the testExperimenter may follow up with

questions about interaction– Likes, dislikes, comments, suggestions

for system improvements, etc.• Verbally (individual interview)

– Structured or semi-structured• Questionnaire with both closed and open-

ended questions

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DebriefingDebriefing

Experimenter ensures that data collected from each user are labeled– User is given a code or number for

identification purposes Experimenter writes a brief preliminary

report while events are still fresh Collected data are coded, analyzed,

interpreted, and reported