Evaluating User Interfaces Walkthrough Analysis Joseph A. Konstan [email protected].
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Transcript of Evaluating User Interfaces Walkthrough Analysis Joseph A. Konstan [email protected].
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Interface Development Methodology Prototype and Iterate
keep iterating until it is good enough
evaluate along the way to assess What is Good? What is Good
Enough? set usability goals should relate to tasks
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Casual Iteration
Find major usability problems missing features user confusion poor interaction
Try interface with specific tasks first use designers, then move
towards users observe overall usage
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Casual Iteration
Remember the goal don’t defend the interface don’t bias the tests towards the
interface If possible, allow user exploration
may even lead to capturing new tasks
Consider alternative ways to fix a problem
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Limits of Casual Iteration Does not indicate when to stop Financial trade-offs Justification of delay
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Usability Goals and Measures Concrete, quantitative measures of
usability learning time use time for specific tasks and users error rates measures of user satisfaction
Comparative usability goals compare with prior versions or
competitors
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Things to Watch
Goals should be realistic 100% is never realistic
Many goals go beyond the application UI training, manuals
Testing goals should help improve the UI detail--not just good/bad
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Exercise:Setting Usability Goals In project groups, come up with 2
usability goals for your project discuss the feasibility of testing these
goals what is needed for the test when in the process can they be
tested? how much effort, user
preparation/training, etc.? what would you learn from the test?
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Interface Evaluation
Goals of interface evaluation find problems find opportunity for improvement determine if interface is “good
enough”
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With or Without Users
Users are expensive and inconsistent usability studies require several
users some users provide great
information, others little Users are users
cannot be simulated perfectly Best choice--Both
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Evaluation Without Users Quantitative Methods
GOMS/keystroke analysis back-of-the-envelope action
analysis Qualitative Methods
expert evaluation cognitive walkthrough heuristic evaluation
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Walkthrough Analysis
Economical interface evaluation low-fidelity prototype development team
users optional Effective, if
goal is improvement, not defense some team members skilled proper motivation
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Cognitive Walkthrough
Goals imagine user’s experience evaluate choice-points in the interface detect confusing labels or options detect likely user navigation errors
Start with a complete TCUID scenario never try to “wing it” on a walkthrough
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Tell a Believable Story
How does the user accomplish the task
Action-by-action Based on user knowledge and
system interface
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Best Approach
Work as a group don’t partition the task
Be highly skeptical remember the goal!
Every gap is an interface problem
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Who Should Do the Walkthrough Designers, as an early check Team of designers & users
remember: goal is to find problems
avoid making it a show Skilled UI people may be valuable
team members
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How Far Along
Basic requirements description or prototype of interface know who users are (and their experience) a task description a list of actions to complete the task
(scenario) DO NOT try to create the action list on the fly!
Viable once the scenario and interface sketch are completed
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How to Proceed
For each action in the sequence tell the story of why the user will do it ask critical questions
will the user be trying to produce the effect? will the user see the correct control? will the user see that the control produces the
desired effect? will the user select a different control instead? will the user understand the feedback to
proceed correctly?
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Walkthroughs are not Perfect
They won’t find every problem limited by nature
new users who know what task they need to accomplish
biased towards correct action sequence limited in implementation
hard to shed the expertise of evaluators A useful tool in conjunction with others
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Exercise: Cognitive Walkthrough Analysis In non-project groups of 3-5 Users and Task to be announced Scenario developed jointly Perform walkthrough
identify problems estimate error probabilities (25%
intervals) Remember who your users are!
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GOMS/Keystroke Analysis Formal action analysis
accurately predict task completion time for skilled users
Break task into tiny steps keystroke, mouse movement,
refocus gaze retrieve item from long-term memory
Look up average step times tables from large experiments
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GOMS/Keystroke Analysis Primary utility: repetitive tasks
e.g., telephone operators benefit: can be very accurate (within
20%) may identify bottlenecks
Difficulties challenging to decompose accurately long/laborious process not useful with non-experts
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Back-of-the-Envelope Action Analysis Coarse-grain
list basic actions (select menu item) each action is at least 2-3 seconds what must be learned/remembered? what can be done easily? documentation/training?
Goal is to find major problems Example: 1950’s 35mm camera
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Expert Evaluation
Usability specialists are very valuable double-specialists are even better
An inexpensive way to get a lot of feedback
Be sure the expert is qualified in your area