CS 430 / INFO 430
Information Retrieval
Lecture 23
Usability 2
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Course Administration
Wednesday, November 16
No discussion class
Thursday, November 17
No lecture
No office hours
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Course Administration
Assignment 3
Grades were returned yesterday
If you have any questions, send email to
cs430-l@lists.cs.cornell.edu
Replies may be delayed until next week
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Usability Factors in Searching
Example: Design an interface for a simple fielded search.
Interface: Fill in boxes, text string, ... ?
Presentation of results ... ?
Manipulation of results ... ?
Functions: Specify field(s), content, operators, ... ?
Retain results for manipulation ... ?
Query options ... ?
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Data:
Metadata formats ... ?
Data structures and file structures ... ?
Systems:
Performance ... ?
The Design/Evaluate Process
Requirements
(needs of users
and other
stakeholders)
Evaluation
start
Implementation
(may be prototype)
release
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Design (creative
application of
design principles)
Evaluation
What is usability?
Usability comprises the following aspects:
• Effectiveness – the accuracy and completeness with which
users achieve certain goals
Measures: quality of solution, error rates
• Efficiency – the relation between the effectiveness and the
resources expended in achieving them
Measures: task completion time, learning time, clicks number
• Satisfaction – the users’ comfort with and positive attitudes
towards the use of the system
Measures: attitude rating scales
From ISO 9241-11
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Evaluation
• The process of determining the worth of, or assigning a
value to, the usability on the basis of careful examination
and judgment.
• Making sure that a system is usable before launching it.
• Iterative improvements after launch.
• Categories of evaluation methods:
– Analytical evaluation: without users
– Empirical evaluation: with users
– Measurements of operational systems
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Evaluation without Users
Assessing systems using established theories and methods
Evaluation techniques
• Heuristic Evaluation (Nielsen, 1994)
– Evaluate the design using “rules of the thumb”
• Cognitive Walkthrough (Wharton et al, 1994)
– A formalized way of imagining people’s thoughts and
actions when they use the interface for the first time
• Claims Analysis – based on scenario-based analysis
– Generating positive and negative claims about the
effects of features on the user
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Evaluation with Users
Testing the system, not the users!
Stages of evaluation with users:
Preparation
Sessions conduct
Analysis of results
User testing is time-consuming and expensive.
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Evaluation with Users
Preparation
• Determine goals of the usability testing
“The user can find the required information in no more
than 2 minutes”
• Write the user tasks
“Answer the question: how hot is the sun?”
• Recruit participants
Use the descriptions of users from the requirements phase
to detect potential users
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Usability Laboratory
Concept: monitor users while they use system
Evaluators
one-way
mirror
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User
Evaluation with Users
Sessions Conduct
• Conduct the session
– Usability Lab
– Simulated working
environment
• Observe the user
– Human observer(s)
– Video camera
– Audio recording
• Inquire satisfaction data
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Evaluation with Users
Results Analysis
• If possible, use statistical summaries
• Pay close attention to areas where users
– were frustrated
– took a long time
– couldn't complete tasks
• Respect the data and users' responses, don't make excuses
for designs that failed
• Note designs that worked and make sure they're
incorporated in the final product
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Measurements on operational systems
Analysis of system logs
• Which user interface options were used?
• When was was the help system used?
• What errors occurred and how often?
• Which hyperlinks were followed (click through data)?
Human feedback
• Complaints and praise
• Bug reports
• Requests made to customer service
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The Search Explorer Application:
Reconstruct a User Sessions
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Refining the design based on
evaluation
Designers and evaluators need to work as a team
Designers are poor evaluators of their own work, but know the
requirements, constraints, and context of the design:
• Some user problems can be addressed with small changes
• Some user problems require major changes
• Some user requests (e.g., lots of options) are incompatible
with other requests (e.g., simplicity)
Do not allow evaluators to become designers
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Usability experiment:
Ordering of results
The order in which the hits are presented to the user:
• Ranked by similarity of match (e.g., term weighting)
• Sorted by a specified field (e.g., date)
• Ranked by importance of document as calculated by some
algorithm (e.g., Google PageRank)
• Duplicates shown separately or merged into a single record
• Filters and other user options
What impact do these choices have on the usability?
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Experiment on the Google Interface
Methodology
• 10 information seeking tasks in 2 categories
• Users randomized across tasks
• Click-through data to see what the user did
• Eye tracking data to see what the user viewed
• Google results presented with top ten ranks reversed
An example of interdisciplinary information science
research by Cornell's Human Computer Interaction
Group and Computer Science Department
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Evaluation Example: Eye Tracking
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Evaluation Example: Eye Tracking
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Google Evaluation
Click-Through Data
Number of users who
clicked on link
Rank of hit
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Google Evaluation
Eye Tracking Data
Number of users who viewed
short record before first click
350
300
250
200
150
100
50
0
1
2
3
4
Rank of hit
22
5
6
7
8
9
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Google Evaluation:
Eye Tracking Data
Part of short record viewed before first click (% of users)
Title: 17.4%
Snippet: 42.1%
Category: 1.9%
URL: 30.4%
Other: 8.2% (includes, cached, similar pages, description)
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Google Experiment: Click Through
Data with Ranks Reversed
ChosenRank
Percentage of users
who clicked on link
Cond: r
80
Percent
60
40
20
0
1
2
3
4
5
ChosenRank
6
Rank of hit
24
8
9
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