IAT 334

Experimental Evaluation

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SCHOOL OF INTERACTIVE ARTS + TECHNOLOGY [SIAT] | WWW.SIAT.SFU.CA

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Evaluationg Evaluation stylesg Subjective data

– Questionnaires, Interviewsg Objective data

– Observing Users• Techniques, Recording

g Usability Specifications– Why, How

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Our goal?

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Evaluationg Earlier:

– Interpretive and Predictive• Heuristic evaluation, walkthroughs,

ethnography…

g Now:– User involved

• Usage observations, experiments, interviews...

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Evaluation Formsg Summative

– After a system has been finished. Make judgments about final item.

g Formative– As project is forming. All through the

lifecycle. Early, continuous.

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Evaluation Data Gatheringg Design the experiment to collect the

data to test the hypothesis to evaluate the interface to refine the design

g Information we gather about an interface can be subjective or objective

g Information also can be qualitative or quantitative– Which are tougher to measure?

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Subjective Datag Satisfaction is an important factor in

performance over time

g Learning what people prefer is valuable data to gather

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Methodsg Ways of gathering subjective data

– Questionnaires– Interviews– Booths (eg, trade show)– Call-in product hot-line– Field support workers

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Questionnairesg Preparation is expensive, but

administration is cheapg Oral vs. written

– Oral advs: Can ask follow-up questions– Oral disadvs: Costly, time-consuming

g Forms can provide better quantitative data

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Questionnairesg Issues

– Only as good as questions you ask– Establish purpose of questionnaire– Don’t ask things that you will not use– Who is your audience?– How do you deliver and collect

questionnaire?

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Questionnaire Topicg Can gather demographic data and

data about the interface being studied

g Demographic data:– Age, gender– Task expertise– Motivation– Frequency of use– Education/literacy

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Interface Datag Can gather data about

– screen– graphic design– terminology– capabilities– learning– overall impression– ...

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Question Formatg Closed format

– Answer restricted to a set of choices

Characters on screen

hard to read easy to read 1 2 3 4 5 6 7

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Closed Formatg Likert Scale

– Typical scale uses 5, 7 or 9 choices– Above that is hard to discern– Doing an odd number gives the neutral

choice in the middle

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Closed Formatg Advantages

– Clarify alternatives– Easily quantifiable– Eliminates useless answers

g Disadvantages– Must cover whole range– All should be equally likely– Don’t get interesting, “different”

reactions

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Issuesg Question specificity

– “Do you have a computer?”g Language

– Beware terminology, jargong Clarityg Leading questions

– Can be phrased either positive or negative

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Issuesg Prestige bias

– People answer a certain way because they want you to think that way about them

g Embarrassing questionsg Hypothetical questionsg “Halo effect”

– When estimate of one feature affects estimate of another (eg, intelligence/looks)

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Deploymentg Steps

– Discuss questions among team– Administer verbally/written to a few

people (pilot). Verbally query about thoughts on questions

– Administer final test

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Open-ended Questionsg Asks for unprompted opinionsg Good for general, subjective

information, but difficult to analyze rigorously

g May help with design ideas– “Can you suggest improvements to this

interface?”

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Ethicsg People can be sensitive about this process

and issuesg Make sure they know you are testing software, not them

g Attribution theory – Studies why people believe that they

succeeded or failed--themselves or outside factors (gender, age differences)

g Can quit anytime

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Objective Datag Users interact with interface

– You observe, monitor, calculate, examine, measure, …

g Objective, scientific data gatheringg Comparison to interpretive/predictive

evaluation

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Observing Usersg Not as easy as you think

g One of the best ways to gather feedback about your interface

g Watch, listen and learn as a person interacts with your system

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Observationg Direct

– In same room– Can be intrusive– Users aware of

your presence– Only see it one

time– May use

semitransparent mirror to reduce intrusiveness

g Indirect– Video recording– Reduces intrusiveness, but doesn’t

eliminate it– Cameras focused on screen, face &

keyboard– Gives archival record, but can spend a

lot of time reviewing it

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Locationg Observations may be

– In lab - Maybe a specially built usability lab• Easier to control• Can have user complete set of tasks

– In field• Watch their everyday actions• More realistic• Harder to control other factors

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Challengeg In simple observation, you observe

actions but don’t know what’s going on in their head

g Often utilize some form of verbal protocol where users describe their thoughts

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Verbal Protocolg One technique: Think-aloud

– User describes verbally what s/he is thinking and doing• What they believe is happening• Why they take an action• What they are trying to do

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Think Aloudg Very widely used, useful techniqueg Allows you to understand user’s

thought processes better

g Potential problems:– Can be awkward for participant– Thinking aloud can modify way user

performs task

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Teamsg Another technique: Co-discovery

learning– Join pairs of participants to work

together– Use think aloud– Perhaps have one person be semi-

expert (coach) and one be novice– More natural (like conversation) so

removes some awkwardness of individual think aloud

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Alternativeg What if thinking aloud during session

will be too disruptive?g Can use post-event protocol

– User performs session, then watches video afterwards and describes what s/he was thinking

– Sometimes difficult to recall

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Historical Recordg In observing users, how do you

capture events in the session for later analysis?

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Capturing a Sessiong 1. Paper & pencil

– Can be slow– May miss things– Is definitely cheap and easy

Time 10:00 10:03 10:08 10:22

Task 1 Task 2 Task 3 …

Se

Se

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Capturing a Sessiong 2. Audio tape

– Good for talk-aloud– Hard to tie to interface

g 3. Video tape– Multiple cameras probably needed– Good record– Can be intrusive

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Capturing a Sessiong 4. Software logging

– Modify software to log user actions– Can give time-stamped key press or

mouse event– Two problems:

• Too low-level, want higher level events• Massive amount of data, need analysis tools

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Assessing Usabilityg Usability Specifications

– Quantitative usability goals, used a guide for knowing when interface is “good enough”

– Should be established as early as possible in development process

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Measurement Processg “If you can’t measure it, you can’t

manage it”

g Need to keep gathering data on each iterative refinement

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What to Measure?g Usability attributes

– Initial performance– Long-term performance– Learnability– Retainability– Advanced feature usage– First impression– Long-term user satisfaction

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How to Measure?g Benchmark Task

– Specific, clearly stated task for users to carry out

g Example: Calendar manager– “Schedule an appointment with Prof.

Smith for next Thursday at 3pm.”

g Users perform these under a variety of conditions and you measure performance

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Assessment TechniqueUsability Measure Value to Current Worst Planned Best poss Observattribute instrument be measured level acc level target level level results

Initial Benchmk Length of 15 secs 30 secs 20 secs 10 secs perf task time to (manual) success add appt on first trial

First Quest -2..2 ?? 0 0.75 1.5impression

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Summaryg Measuring Instrument

– Questionnaires– Benchmark tasks

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Summaryg Value to be measured

– Time to complete task– Number of percentage of errors– Percent of task completed in given time– Ratio of successes to failures– Number of commands used– Frequency of help usage

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Summaryg Target level

– Often established by comparison with competing system or non-computer based task

Ethicsg Testing can be arduousg Each participant should consent to

be in experiment (informal or formal)– Know what experiment involves, what to

expect, what the potential risks are g Must be able to stop without danger

or penaltyg All participants to be treated with

respectNov 2, 2009 IAT 334 42

Consentg Why important?

– People can be sensitive about this process and issues

– Errors will likely be made, participant may feel inadequate

– May be mentally or physically strenuousg What are the potential risks (there are

always risks)?– Examples?

g “Vulnerable” populations need special care & consideration (& IRB review)– Children; disabled; pregnant; students (why?)Nov 2, 2009 IAT 334 43

Before Studyg Be well prepared so participant’s time is

not wastedg Make sure they know you are testing

software, not them– (Usability testing, not User testing)

g Maintain privacyg Explain procedures without compromising

resultsg Can quit anytimeg Administer signed consent formNov 2, 2009 IAT 334 44

During Study Make sure participant is comfortable Session should not be too long Maintain relaxed atmosphere Never indicate displeasure or anger

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After Study State how session will help you improve

system Show participant how to perform failed

tasks Don’t compromise privacy (never identify

people, only show videos with explicit permission)

Data to be stored anonymously, securely, and/or destroyed

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One Model