CS3724 Human-computer Interaction
Usability
Specifications
Copyright © 2004 H. Rex Hartson and Deborah Hix.
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Usability Specifications in the Human Computer Interactions | CS 3724, Study notes of Computer Science
Material Type: Notes; Class: Human-Computr Intrctn; Subject: Computer Science; University: Virginia Polytechnic Institute And State University; Term: Summer I 2004;
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CS3724 Human-computer Interaction
UsabilitySpecificationsCopyright © 2004 H. Rex Hartson and Deborah Hix.
Topics
z
What are usability specifications?
z
Usability specification tables
z
Benchmark task descriptions
z
User errors in usability specifications
z
Usability specifications and managing the UEprocess
z
Team exercises
Usability Specifications
z
Tie usability specifications to early usabilitygoals
E.g., for early goal of walk-up-and-use usability, baseusability specification on initial task performance time
z
All project members should agree on usabilityspecifications attribution and values
Usability Specification Data
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Usability specifications based on
Objective
, observable user
performance
Subjective
, user opinion and
satisfaction
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Subjective preferences may reflect usersdesire to return to your Web site, but flashand trash soon bores and irritates
z
Objective and subjective usabilityspecifications can both be quantitative
Usability Specifications
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Some quantitative usability attributes
Objective
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Initial performance (on benchmark tasks)
z
Longitudinal (experienced, steady state) performance
z
Learnability
z
Retainability
Subjective
z
Initial impression (questionnaire score)
z
Longitudinal satisfaction
Usability Specification Table
z
Usability attribute for Calendar
Initial performance, since want good 'walk-up-and-usperformance w/o training or manuals
Initialperformance
Target
level
Current
level
Value to be
measured
Measuring instrument
Usability
attribute
Benchmark Tasks
z
What tasks should be included?
Representative, frequently performed tasks
Common tasks – 20% that account for 80% ofusage
Critical business tasks – not frequent, but if youget it wrong, heads can roll
z
Example: Schedule a meeting with Dr. Ehrichfor four weeks from today at 10 am in 133McBryde, about the HCI research project
Benchmark Task Descriptions
z
Clear, precise, repeatable instructions
z
IMPORTANT
: What task to do, not how to do it
z
Clear start and end points for timing
Not: Display next week’s appointments (end with a usaction confirming end of task)
z
Adapt scenarios already developed for design
Clearly an important task to evaluate
Remove information about how to do it
Benchmark Task Descriptions z
Tasks wording should be unambiguous
Why is this ambiguous? “Schedule a meeting withMr. Jones for one month from today, at 8 AM.”
z
Important
: Don’t use words in benchmark
tasks that appear specifically in interactiondesign
Not: “Find first appointment …” when there is abutton labeled “Find”
Instead: use “search for”, “locate”
Benchmark Task Descriptions z
Use work context wording, not system-oriented wording
“Access information about xyz” is betterthan “submit query”
z
To evaluate error recovery, benchmarktask can begin in error state
Usability Specification Table
BT1: Addappt
Initialperformance
Target leve
Current
level
Value to be
measured
Measuring instrument
Usability
attribute
Usability Specification Table
z
Value to be measured
- metric for which usability data
values are collected
BT1: Addappt
Initialperformance
Target leve
Current
level
Value to be
measured
Measuring instrument
Usability
attribute
Usability Specification Table
Time on task
BT1: Addappt
Initialperformance
Target leve
Current
level
Value to be
measured
Measuring instrument
Usability
attribute
Usability Specification Table
Time on task
BT1: Addappt
Initialperformance
Target leve
Current
level
Value to be
measured
Measuring instrument
Usability
attribute
z
Current level
- present value of usability
attribute to be measured