usability

1. Usability and Evaluation
 Usability and evaluation are closely related
concepts
 Usability means that the HCI design of the
system supports the user’s cognitive
limitations and is easy to use and learn
 Evaluation means to assess the system for
functionality as well as usability

2.  Designers of the OMS (Olympic
Message System) followed 3 principles:
– Early focus on user and tasks
– Empirical measure on user’s behavior
– Iterative design
Usability and Evaluation

3. Usability and Evaluation
Attitudes, use, performance, and satisfaction
relationship

4.  ISO (International Standards
Organization) defines usability as “ a
concept comprising the effectiveness,
efficiency, and satisfaction with which
specified users can achieve specified
goals in a particular environment”
Usability and Evaluation

5. Usability and Evaluation
Usability indicators based on performance
1. Goal achievement indicators (success rate, failure rate,
accuracy, effectiveness).
2. Work rate indicators (speed, completion rate, efficiency,
productivity, productivity gain).
3. Operability indicators of the user's ability to make use of the
systems features (error rate, problem rate, function usage)
4. Knowledge indicators of the user's ability and effort in
learning to use the system (learnability and learning).

6. Usability and Evaluation
Usability measures based on performance and HCI
1. Time to complete a task
2. Number of user commands to complete task
3. Fraction of task completed
4. Fraction of task completed in a given time
5. Number of errors
6. Time spent on errors
7. Frequency of online help used
8. Number of available commands not used
9. When task is repeated, ratio of successes to failures
10. Fraction of positive comments made by user
11. Fraction of good to bad features recalled by user
12. Number of expressions of frustration and satisfaction
13. Number of times user loses control over system
14. Number of times the user needs to devise a way of working around the
problem/system.

7. Usability and Evaluation
The usability engineering life cycle
· Know the user
· Analyze competing products
· Set usability goals
· Consider alternative designs
· Engage in participatory design
· Coordinate the total interface
· Check against heuristic guidelines
· Prototype
· Evaluate interface
· Design in iterations
· Follow up with studies of installed systems

8.  Methods of usability assessments
include:
– Thinking aloud (protocol analysis)
– Observation
– Interviews
– Focus groups
– Automatic logs
– Questionnaires
Usability and Evaluation

9. Usability and Evaluation
1. Create simple and natural dialog
2. Speak the user's language
3. Minimize the user's memory load
4. Be consistent
5. Provide feedback
6. Provide clearly marked exits
7. Provide shortcuts
8. Provide specific, corrective and positive error messages
9. Minimize error

10.  Evaluation is a broader term than usability – it
includes several goals:
1) assess the system's functionality against
the intended specifications,
2) assess the system's effect on the user's
behavior and attitude,
3) assess the system's impact on measures
of performance that are related to the user or
the objective of the system,
4) discover unintended problems and
perhaps opportunities.
Usability and Evaluation

11. Usability Testing
 Usability testing refers to evaluating a
product or service by testing it with
representative users. Typically, during a
test, participants will try to complete typical
tasks while observers watch, listen and
takes notes.

12.  The goal is to identify any usability
problems, collect qualitative and
quantitative data and determine the
participant's satisfaction with the product

13. Benefits of Usability Testing
Usability testing lets the design and
development teams identify problems
before they are coded. The earlier issues are
identified and fixed, the less expensive the
fixes will be in terms of both staff time and
possible impact to the schedule. During a
usability test, you will:

14.  Learn if participants are able to complete
specified tasks successfully and
 Identify how long it takes to complete
specified tasks
 Find out how satisfied participants are with
your Web site or other product

15.  Identify changes required to improve user
performance and satisfaction
 And analyze the performance to see if it
meets your usability objectives