What
is usability?
User
friendly
–No need m/c to friendly
Different users have different needs
A system that is “friendly” to one may feel very tedious to another
–No need m/c to friendly
Different users have different needs
A system that is “friendly” to one may feel very tedious to another
•Use
other terms
–CHI
–HCI
–UCD
–MMI
–HMI
–OMI
–UID
–HF
–Etc
System
Acceptability
•Social
acceptability
•Practical
acceptability
Definition
of Usability
•5
usability attributes:
–Learnability
–Efficiency
–Memorability
–Errors
–Satisfaction
Learnability
•The
system should be easy to learn for
novice users
•Highly
learnable systems have a steep incline for the first part of the learning curve
and allow users to reach a reasonable level of usage proficiency within a short
time
•Zero
efficiency at zero time except walk-up-and-use systems
•Easy
to measure
Efficiency
of Use
•The
system should be efficient to use for expert users, so that once the users has
learned the system, a high level of productivity is possible
•Test
users are asked to use the system for a certain number of hours, after their
efficiency can be measured
–In terms of number of seconds to do
a specific task
Memorability
•The
system should be easy to remember, so that casual user is able to return to the
system after some period of not having used it, without having to learn
everything all over again
•“Kiss
and Ride”
•2
ways of measuring
–Measure the time needed for casual
users to perform some typical test tasks
–Memory test
•After finishing the test session
explain the effect of various commands or name the command
Few
and non catastrophic errors
•The
system should have a low error rate, so that users make few errors during the
use of the system, and so that if they do make errors they can easily recover
from them
•Error
is defined as any action that does not accomplish the desired goal
•Measured
by counting the number of such actions
Subjective
satisfaction
•The
system should be pleasant to use, so that users are subjectively satisfied when
using it; they like it
•Can
be measured by
–Psychophysiological measures
–Asking subjective opinion
•Likert scale
•Please indicate the degree to which
you agree or disagree with the following statements about the system
A.It
was very easy to learn how to use this system
1=strongly
disagree 2=partly disagree 3=neither disagree nor agree 4=partly agree
5=strongly agree
A.Using
this system was a very frustrating experience
B.I
feel that this system allows me to achieve very high productivity
C.I
worry that many of the things I did with this system may have been wrong
D.This
system can do all the things I think I would need
E.This
system is very pleasant to work with
Semantic
differential scale
•Please make the positions that best
reflect your impression of this system
Pleasing - - - - - - - - Irritating
Complete
- - - - - - - - Incomplete
Cooperative - - - - - - - - Uncooperative
Simple
- - - - - - - - Complicated
Fast
to use - - - - - - - - Slow to use
Safe
- - - - - - - - Unsafe
