1 Usability Guidelines, Principles & Theories Lecture 6 Date: 16 th February.

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Usability Guidelines, Principles &

TheoriesLecture 6

Date: 16th February

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Overview of Lecture

•Principles

•Principles of Universal Design

•Major design principles

•Nielsen’s usability principles

•Theories

•GOMs

•7 Stages-of-Action

•Levels of Analysis

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Design Principles

•A number of design principles have been promoted

•They are concerned with how to determine what users should see and do

•6 major design principles have been identified (written about extensively in Norman’s Design of Everyday Things)

Principles

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Design Principles

•Visibility

•Feedback

•Constraints

•Mapping

•Consistency

•Affordance//Will be discussed in conjunction with usability principles

Principles

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Usability Principles

•Nielsen defined 10 usability principles that can be applied to any system, although frequently used for web applications

•Similar in aim to usability goals, except more slightly more prescriptive

•Used mainly as the basis for evaluating systems

•Provide a framework for usability evaluation

Principles

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Usability Principles

•Visibility of system status •Match between system and the real world •User control and freedom •Consistency and standards.•Help users recognize, diagnose and recover from errors •Error prevention •Recognition rather than recall •Flexibility and efficiency of use •Aesthetic and minimalist design •Help and documentation

Principles

7Principles

Usability/Design Principles

Visibility

Feedback Mapping

Affordance

Consistency

Constraints

Help

Simplicity

User control

error prevention

Consistency

Errors mgt

Recognition

Flexibility

Match to worldVisibilityof status

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1. Visibility of system status Always keep users informed about what is going on, -> provide appropriate timely feedback within reasonable time

• What has been done? • Includes sound, highlighting, animation and combinations

of these

– e.g. when screen button clicked on provides sound or red highlight feedback:

“ccclichhk”

Principles

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Web-site Visibility•The answers to the following questions should be obvious

•where am I?•what can I do?•where will I go if I do this?•where have I been?

•Brand each page

•Show the section it belongs to

•Mark links to other pages clearly.

•Users may jumping to any part of the site from elsewhere you need to include this status on every page.

Principles

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2. Match between system and the real world 1. Speak the users’ language

2. Don’t use system oriented terms

3. Use real world conventions to make information appear in a natural and logical order Use a technique called mapping: Relationship between controls and their movements and the results in the world

Principles


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•Why is this a poor mapping of control buttons?

•Why is this a better mapping

Principles


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3. User control and freedom

Provide ways of allowing users to easily escape and navigate to/from places they unexpectedly find themselves e.g.

• page forward / backward• hold• cancel• end / stop• help• resume• undo

Principles


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•Need a clearly marked "emergency exit”•Users can choose system functions by mistake•Need to escape from an unwanted state without having to go through an extended dialogue. •Need to support undo and redo.

•Browser provides "emergency exits” but you can supply your own buttons to support user control and freedom.

•Can take away user control built into the Web.

• A "home" button on every page •simple way to let users feel in control of your site.

Principles


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4. Consistency and standards

Avoid making users wonder whether different words, situations or actions means the same thing

• Design interfaces to have similar operations and use similar elements for similar tasks

• Main benefit is consistent interfaces are easier to learn, use and remember

Principles


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Example:

Use consistent wording in your content and buttons.

• Most common inconsistency is between page titles and page headers for pages, and the links to them.

• Destination page’s title different from the link that took user there leads to user confusion.

• Other examples:• always use ctrl key plus first initial of the command

for an operation – ctrl+C, ctrl+S, ctrl+O

Principles


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• Follow platform conventions• Avoid confusion over whether different

words, situations, or actions mean the same thing to user

• No custom link colours. They may conflict with rest of Web and make site hard to use.

• Web "standards" • Follow HTML specifications• Deviations from the standards results in

unusable features creeping in

Principles


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Internal and external consistency• Internal consistency refers to designing

operations to behave the same within an application

• Difficult to achieve with complex interfaces

• External consistency refers to designing operations, interfaces, etc., to be the same across applications and devices

• Difficult to ensure across different types of devices - Based on different designer’s preference. Can be dictated by corporate guidelines

Principles


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• A case of external inconsistency

1 2 3

4 5 6

7 8 9

7 8 9

1 2 3

4 5 6

0 0

(a) phones, remote controls(a) phones, remote controls (b) calculators, computer keypads(b) calculators, computer keypads

Principles


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5. Help users recognize, diagnose and recover from errors

Use plain language to describe the nature of the problem and suggest a way of solving it

• Careful design is better than good error messages

• prevents problems from occurring in the first place

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• Detection• immediately detect all errors• maintain the item in error• visually highlight the item in error• identify field requiring missing data• display error messages on the screen• position cursor at first error• use auditory signals conservatively

• Correction• provide constructive error messages

• what error was detected• which field was in error• what corrective action is necessary

• resend only erroneous information back to system

Principles


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6. Recognition rather than recall

Make objects, actions, and options visible. • Don’t force user to recall information • Instructions should be visible or retrieved easily when

needed.

• From point of view of the Web, this heuristic is closely related to system status

• Users won’t get lost if they can see where they are by looking at clues given by on current page.

• No need to recall their path to the home page.• Good labels & descriptive links are essential for

recognition. • Use images for links, but they need to be well designed.

Principles


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Recognition vs recall uses concept of Affordance

• Refers to an attribute of an object that allows people to know how to use it

• Much popularised term in interaction design to discuss how to design interface objects• e.g. scrollbars to afford moving up and down,

icons to afford clicking on

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7. Error prevention

Prevent them occurring in first place if possible

Key question: Does the system prevent users from making serious errors, and if they do make an error, does it permit them to recover easily

• Prevention• permit review of message about to be sent

• handle common misspellings

• permit editing of message about to be sent• advise of non-reversible changes

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• Constraints (for error prevention)

• permit review of message about to be sent• handle common misspellings• permit editing of message about to be sent• Restricting the possible actions that can be

performed• Helps prevent user from selecting incorrect

options• Three main types (Norman, 1999)

• Physical – (discussed in next side)

• cultural - e.g. culture• Logical – e.g. menu item ordering

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• Physical Constraints

• Refer to the way physical objects restrict the movement of things

• E.g. only one way you can insert a key into a lock

• How many ways can you insert a CD or DVD disk into a computer?

• How physically constraining is this action?• How does it differ from the insertion of a floppy disk

into a computer?

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8. Flexibility and efficiency of use

Provide accelerators that are invisible to novice users, but allow more experienced users to carry out tasks more quickly:

• Use accelerators (keyboard shortcuts)

• Web Browser provides good accelerators e.g. bookmarks

• Design for effective book-marking• contents of site can easily be linked to • users create specialized views of a site for specific tasks

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9. Aesthetic and minimalist design

Avoid using info that is irrelevant or rarely needed

• No irrelevant or rarely needed information in dialogues -> diminishes visibility

• Extraneous information on a page distracts user & slows them down.

• Use progressive levels of detail.

• Support different uses of content. No brochures.

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10.Help and documentation

Provide information that can be easily searched and provides help in a set of concrete steps that can easily be followed

• Better if the system can be used without documentation

• it may be necessary to provide help and documentation• Make it easy to search, focused on the user's task,• list concrete steps to be carried out, and not too large.

Principles


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Pros and Cons: Heuristic Evaluation

AdvantagesAdvantagesdetects both major (42%) and minor (32%) problems in UI

more effective than single specialist

can be used on designs

“realistic” approach

“severity rating” helps to set priorities

DisadvantagesDisadvantagesgroups can develop their own bias

doing it properly is not that cheap

new technologies (Web, Multimedia, Virtual Reality) may have specific problems not covered by The Heuristics

Principles

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Theories

• Beyond the specifics of guidelines

• Principles are used to develop theories

• 3 examples of theories:• Levels of Analysis model• Stages of action models• GOMS and the keystroke-level model

Theories

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Levels of Analysis Model• Foley and van Dam four-level approach

• Conceptual level: user’s mental model of system

• Semantic level: meaning conveyed by input/output

• Syntactic level: assembly of actions to perform tasks

• Lexical level: device level actions

• Approach is convenient for designers

• Top-down nature is easy to explain

• Matches the software architecture

• Allows for useful modularity during design

Theories

Device/Tooldependent

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Stages of Action Model

• Norman's seven stages of action 1. Forming the goal 2. Forming the intention 3. Specifying the action 4. Executing the action 5. Perceiving the system state 6. Interpreting the system state 7. Evaluating the outcome

• Norman's contributions • Context of cycles of action and evaluation. • Gulf of execution: Mismatch between the user's

intentions and the allowable actions • Gulf of evaluation: Mismatch between the system's

representation and the users' expectations

Theories

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Theories

THE WORLD

Goals

Intention to act

Sequence of actions

Execution of theAction sequence

Evaluation ofinterpretations

Interpreting theperception

Perceiving the stateof the world

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2

3

7

6

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Theories

1. Form the Goal

3. Specify action

ConceptualModel(Goals)

2. Intention 4. Execute action

Real World(Interactions)

5. Perceive system state

6. Interpret

7. Evaluate

Cycle of Execution

Cycle of Evaluation

Gulf

Gulf of execution: Mismatch between the user's intentions and the allowable actions

Gulf of evaluation: Mismatch between the system's representation and the users' expectations

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• Four principles of good designFour principles of good design • State and the action alternatives should be visible • Should be a good conceptual model with a consistent

system image • Interface should include good mappings that reveal the

relationships between stages • User should receive continuous feedback

• Four critical points where user failures can occurFour critical points where user failures can occur • Users can form an inadequate goal • Might not find the correct interface object because of an

incomprehensible label or icon • May not know how to specify or execute a desired

action • May receive inappropriate or misleading feedback

Theories

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GOMS and the keystroke-level model

• Goals and sub-goals

• Operators: “elementary perceptual, motor or cognitive acts”

• Methods: actions

• Selection rules: control structures for decisions between methods

Theories

(Card, Moran and Newell, 1980)

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Keystroke level model (KLM)Card, Moran and Newell (1980)

• Purpose• approximate prediction of time to perform tasks• allows comparison between alternative design

options• applicable in principle to any interactive system

• Assumptions• routine tasks• expert, error-free performance• assumes knowledge of task/sub-tasks; method

used for task; and some information about the system

Theories

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Content of the model

• a description of the task• a simple model of the user• a simple model of the computer

• tasks are executed by a sequence of operators - physical actions of the user and computer

� Texecute = TK + TP + TH + TD + TM + TR

� where K = keystroking; P = pointing; H = homing; D = drawing; M = mental operator; R = system response operator

Theories

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KLM ExamplesFrom Card et al 1980

–Method for task T1-Disped–Reach for mouse H[mouse)

–Point to word P[word]

–Select word K[YELLOW]

–Home on keyboard H[keyboard]

–Call replace command MK[R]

–Type new 5-digit word 5K[word]

–Terminate type-in MK[ESC]

»Texecute = 2tM + 8tK + 2tH + tP = 6.2s

»Method for Task T1-Poet�Jump to next line MK[LINEFEED]

�Call substitute command MK[S]

�Specify new 5-digit word 5K[word]

�Terminate argument MK[RETURN]

�Specify old 5-digit word 5K[word]

�Terminate argument MK[RETURN]

�Terminate command K[RETURN]

»Texecute = 4tM + 15tK = 8.4 sec.�Assuming tK = 0.2sec.

Conclusion: mouse-basedinteraction is faster

Mouse-based editor

Keyboard-based editor

Theories

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Summary of Lecture• Usability can be defined as the capacity to be used

by humans easily and effectively• Ease-of-use• Friendliness

• Guidelines- provided a number of sample guidelines

• Principles - introduced major principles in HCI• Principles of Universal Design• Major design principles• Nielsen’s usability principles

• Theories - introduced 3 HCI theories• Levels of Analysis • 7 Stages-of-Action• GOMS / Keystroke Level Model

References

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Terms of Reference

• Norman, D. (1990) The Design of Everyday Things

• Preece, J. et al. (2002) Interaction Design

• Shneiderman, B. & Plaisant, C. (2005) Designing the User Interface

• Shackel, B. (1990) Human Factors and Usability

• Smith, S. & Mosier, J. (2005) Guidelines for Designing User Interface Software

• Foley, J. & Van Dam, A. (1995) Computer Graphics: Principles & Practices in C

• Card, S. & Newell, A. (1983) The Psychology of Human-Computer Interaction

References

1 Usability Guidelines, Principles & Theories Lecture 6 Date: 16 th February.

Documents

Transcript of 1 Usability Guidelines, Principles & Theories Lecture 6 Date: 16 th February.