Usability Testing

HiØ, Masterstudium InformatikkGrensesnittdesign høsten 2006

Gisle Andresen (gislea@hrp.no) Forsker, Institutt for Energiteknik

Contents

1. Introduction2. Usability measurement3. Data-collection techniques4. Evaluation of usability tests

User-centered design

• A design approach driven by the needs and preferences of users in order to create effective interactive systems

• UCD ensures Usability

Why UCD?

• Negative consequences of not following UCD: poor usability

• reduced effectivity,• human errors,• frustration etc.

http://www.usabilitymustdie.com/usability_review_remote_control.htm

Why UCD?

• Positive consequences of following UCD approach: good usability

• increased effectivity,• Error tolerance,• User satisfaction etc.

Why UCD?

• A reaction against technology- centered design; i.e., design driven by what is technologically possible

• left-over principle: we automate everything possible and leave the rest to the human

Key activities of UCD process

• Identify user needs• Develop prototypes• Perform usability evaluations

Typical project model: Waterfall

UCD and Waterfall

User need ident.

Prototyping

Evaluation

Usability evaluations

• Inspection• Usability testing

Usability testing: characteristics

• Several ”real” users participate

• The users performs realistic tasks

• Measure usability• Use/Problem descriptions

Why several real users?

• Users differ from designers• Users differ from one another

Why realistic tasks?

• Find usability problems of significance to task performance

Why measure?

• Scientific reasons• Pragmatic reasons

Scientic reasons

Everythingthat exists,

exists in someamount

http://serendip.brynmawr.edu/exhibitions/Mind/Images/42.GIF

Pragmatic reasons

• Define specific goals

• Easy to communicateresults

• Allows statistical analysis

• High statushttp://www.usabilitymustdie.com/askJakob.htm

Why Use-/problem descriptions?

• Learn how the system is really used

• Find causes of usability problems

Usability testing approaches (Preece)

• Formative vs. Summative• Quick and dirty vs. Experimental

Usability testing approaches (Rubin)

• Exploratory test• Assessment test• Validation test• Comparison test

What determines the approach?

• Purpose of test• Stage in the design process• Practical limitations

Usability measures

Measure:to assign numbersto objects or attributes according to rules

http://www.psych.utoronto.ca/museum/hippchron.htm

Creating a usability measure

• Select usability attribute• Operationalise criteria• Select data-collection technique

Usability attributes

Efficiency

Effectivity

Satisfaction

Learnability

Memorability

Usefullness

Select attribute

• What attributes are most relevant?

• Important to take into account characteristics of the users, tasks and context

Select attribute: Examples

• Commercial: easy to learn• Entertainment: satisfaction• Seldom used: memorability• Innovative: usefullness• Safety relevant: effective• Complex: efficient

Operationalise criteria

• Can the attribute be ”measured”?• Define a scale• Define acceptance or target

criteria

Operationalise criteria: Example 1

• Effective• Number of tasks performed

correctly• Scale: Summarise the number of

tasks performed and divide by number of possible tasks

• Criteria: All users must perform all important tasks

Operationalise criteria: Example 2

• Efficient• The effort users have to invest in

performing the task• Scale: the more effort, the less

efficient• Criteria: less effort than old

product

http://zing.ncsl.nist.gov/hfweb/proceedings/etgen-cantor/

Operationalise criteria: Example 3

Student tasks

• Can you think of any potential usability problems with your product?

• What is the most important usability attribute for your product?