0. John Stasko John Kelleher
Usability Principles
John Stasko John Kelleher

1. Defining Usability...

2. Five Usability Attributes
Learnability: ease of learning for novice users.
Efficiency: steady-state performance of expert users.
Memorability: ease of using system intermittently for casual users.
Errors: error rate for minor and catastrophic errors.
Subjective Satisfaction: how pleasant system is to use.

3. Learning Curves Some systems are designed to focus on learnability.
Others emphasise efficiency for proficient users.
Some support both ease of learning and an “expert mode”
E.g. Rich menus and dialogues plus a command/scripting language),
Thereby they attempt to ride the top of the curves in next slide.

4. Riding the Learning Curves
Learning curves for hypothetical systems focusing on the novice user (easy to learn, but less efficient to use) and the expert user (harder to learn, but then highly efficient).

5. Typical Ways of Measuring Usability
Learnability: pick novice users of system, measure time to perform certain tasks. Distinguish between no/some general computer experience.
Efficiency: decide definition of expertise, get sample expert users (difficult), measure time to perform typical tasks.
Memorability: get sample casual users (away from system for certain time), measure time to perform typical tasks.
Errors: count minor and catastrophic errors made by users while performing some specified task.
Satisfaction: ask users' subjective opinion (questionnaire, interview), after trying system for real task.1
1 Beware users ratings closely related to ‘peak’ difficulty.

6. UI Usability Principles
Categories
Learnability
support for learning for users of all levels
Flexibility
support for multiple ways of doing tasks
Robustness
support for recovery
Always think about exceptions, suitability

7. Learnability Principles
Predictability
Synthesizability
Familiarity
Generalizability
Consistency

8. Predictability “I think that this action will do….”
Support for the user to determine the effect of future action based on past interaction history
Consequences of current action
Operation visibility –
can see avail actions
e.g. menus vs. command shell
grayed menu items
User does not have to memorize permitted actions
Recognition vs. recall

9. Synthesizability “How did I get here?”
Support for user to assess the effect of past operations
Immediate honesty
Results of actions immediately visible (transparency)
e.g. WIMP file system
Eventual honesty
Results of actions must be inquired
e.g. command line
When an operation changes some aspect of the internal state, it is important that the change is seen by the user. The Principle of honesty relates to the ability of the user interface to provide an observable and informative account of such change.

10. Familiarity “Hey, I think I can figure this out!”
How well the system relates to previous interfaces/experiences
Guessability
e.g. typewriter/word-processor
Affordances
Intrinsic actions of visual objects
e.g. buttons are pushed, ‘rubber’ pads afford dragging
Use of metaphors
pitfalls
Learnability concerns the features of the interactive system that allow the novice users to understand how to operate the system initially and then how to attain a maximal level of performance."(DFAB p.162) This refers to how well the GVU staff, primary users, and students, secondary users, first learn to use then maximize our system. Our users shoulder many responsibilities, they may not be able to allocate time to learn a large and complicated system. Similarly newly hired GVU staff members and new students may also have problems with learning large and complicated systems. Therefore, Learnability at large is an important aspect of our system.
Familiarity, an aspect of Learnability, is well suited for the evaluation of our system. New users may bring a wide range of experiences from different applications to a system. Such is the case with students and GVU staff members, it is important that we utilize these experiences. Our primary and secondary users are proficient computer users. Both of our user groups are familiar with computer desktop application such as word processors and calendar programs, however, our primary user group, the GVU staff members, are more familiar with the dynamics of the surrounding social environment while the students may have more advanced technical knowledge in areas such as programming. For the primary users these experiences are obtained through daily interaction with faculty, students and other systems. For the secondary users, these experiences are obtained through interaction with faculty, other students, classes, and other systems. In order for our design to be successful, it must draw from the users' knowledge and experience. We will observe the Familiarity of our system by doing the following:
Make visual comparisons between the interface of our system and the interface of the existing system.
Determine the length of time required for the GVU staff, our primary users, to adapt to our new interface.
Determine the length of time required for the students, our secondary users, to adapt to our new interface.
Observe how well our users adapt to the new system.
Record if both user groups can adequately interface with our system and what types of mistakes they committed.
Conduct interviews with users to obtain evaluation of our system.

11. Generalisability Does knowledge of one UI apply to others?
Support for user to extend knowledge of specific interaction within and across applications to other similar situations
Analogical mapping
e.g. cut & paste
word processor
file system
UI Developers guidelines

12. Consistency “Just when I get comfortable with a system, it changes!”
Likeness in input-output behaviour arising from similar situations or similar task objectives
Changes in interfaces are disruptive
Need a good reason to change
Otherwise, be consistent
Similar ways of doing tasks
interacting
output
screen layout
Is this always desirable for all systems, all users?

13. Flexibility Principles
“How broad is the interface?”
Dialog Initiative
Multithreading
Task migratability
Substitutivity
Customizability
"Flexibility refers to the multiplicity of ways the end-users and the system exchange information."(DFAB p.167) In the GVU staff's daily activities, much information is exchanged in various forms, word of mouth or , for example. This is also true with our secondary users. In order for our system to be successful, it must increase bidirectional communication between GVU and students, therefore, it must have Flexibility.

14. Dialog Initiative “Who interrupts who?” System pre-emptive
system does all prompts, user responds
sometimes necessary
E.g. “Are you sure you want to do that?”
User pre-emptive
user initiates actions
more flexible
E.g. Buttons, Ctrl-Alt-Del

15. Multithreading “How do I do two things at the same time?”
Support for multiple tasks
Two types
Concurrent
input to multiple tasks simultaneously
Interleaved
many tasks, but input to one at a time
E.g. windowing system

16. Task Migratability “You do that and I’ll do this.”
Division of labour between core and user
E.g. co-operative spell-checking
Ability of user to take control of automated system tasks
E.g. auto-pilot
Task migratability is an aspect of Flexibility. It refers to the transfer of control between a user and a system during a task. Task migratability in our system is indicated by how well the system automate simple tasks. For example, if two events with conflicting schedules are inputed, how well can our system resolve these issue in an automated fashion. This quality is very important to our design since we would like to increase the efficiency and decrease the workload of the GVU events communication system. We must also adhere to the principle of not creating more problems while trying to fix one. We can observe the Task Migratability of our system by:
Record the time required to perform a task on existing system and our system.
Observe if there were pauses during the task and for what reason.
Observe if the system's automated processes create any interferences for the users.
Conduct interviews with users to obtain evaluation of our system.

17. Substitutivity “What format should I use?”
I/O should be available in multiple redundant forms
Allow user to choose suitable interaction methods
Allow different ways to
perform actions E.g. Excel
specify data
configure
Allow different ways of presenting output
to suit task, user
E.g. PowerPoint normal view, notes view, slide sorter, print preview etc.

18. Customizability “How can I make this interface work better?”
Ability to modify interface
By user - adaptability
E.g. Photoshop actions
By system – adaptivity
E.g. styles in Word

19. Robustness Principles
“How well supported is the interface?”
Observability
Recoverability
Responsiveness
Task Conformance

20. Observability “What is going on?”
Can user determine internal state of system from observable state?
Browsability
explore current state
Reachability
navigate observable states
Persistence
how long does observable state persist?
E.g. Outlook ‘bell’ and system task pane icon

21. Recoverability “Oops!”
Ability to continue to a goal after recognizing error
Forward Recoverability
ability to fix when we can’t undo?
Backward Recoverability
undo previous error(s)
Commensurate effort
Difficult to correct, then difficult to do in the first place

23. Responsiveness “What is the system doing now?” Communication latency
Response time
time for system to respond in some way to user action(s)
Stability principle
response time invariance

24. Task Conformance “This doesn’t do what I need it to do”
Task coverage/completeness
can system do all tasks of interest?
Is it comprehensive?
Task adequacy
How well does it support user’s tasks?
Does system match real-world tasks?
"The robustness of our system covers features which support the successful achievement and assessment of the goals."(DFAB p.172) This is a desired aspect for our system. We would like our system to be able to reach and assess its goals.
Task Conformance an aspect of Robustness. It refers to an interactive system's design to allow users to perform various desired tasks to achieve their goals. We need to determine the task completeness of our system and task adequacy of our system. It is not sufficient that our system fully implements some set of computational services for the GVU staff that were identified in early specification. It is essential that our system provide tools that allows the GVU staff to achieve any desired tasks, new or old, in the domain of event communication. We can measure this principle using the following:
Interview with GVU staff to determine if our system allows them to achieve any of the desired tasks in their work domain of communication.
Observe our users to determine if there were any difficulties or tasks that were not supported by our system.
Record any tasks that is not supported by the current system but is supported by our design.

25. Further Reading
Human-Computer Interaction (2nd Ed.), Chapter 4

26. Novel Answering Machine Interface1
Marbles Answering Machine
Durrell Bishop, while a student at the Royal College of Art (RCA), designed a prototype telephone answering machine to explore ways in which computing can be taken off the desk and integrated into everyday objects. In the marble answering machine, incoming voice messages are physically instantiated as marbles. The user can grasp the message (marble) and drop it into an indentation in the machine to play the message. The user can also place the marble onto an augmented telephone, thus dialing the caller automatically. The original concept animation was followed by several physical prototypes which realized the answering machine along with a family of other physical instantiation of applications.
This physical embodiment of incoming phone messages as marbles demonstrated the great potential of making digital information graspable by coupling bits and atoms.

27. LiveWire1 Marbles Answering Machine
Durrell Bishop, while a student at the Royal College of Art (RCA), designed a prototype telephone answering machine to explore ways in which computing can be taken off the desk and integrated into everyday objects. In the marble answering machine, incoming voice messages are physically instantiated as marbles. The user can grasp the message (marble) and drop it into an indentation in the machine to play the message. The user can also place the marble onto an augmented telephone, thus dialing the caller automatically. The original concept animation was followed by several physical prototypes which realized the answering machine along with a family of other physical instantiation of applications.
This physical embodiment of incoming phone messages as marbles demonstrated the great potential of making digital information graspable by coupling bits and atoms.