User Characteristics & Design Principles

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Lecture # 11

Objective of this lectureDescribe a set of important UI design principlesPlace these principles within the context of

human characteristics and show how they contribute to usability

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Achieving UsabilityOur objective in designing the User Interface is

to achieve a high degree of usability for our product

User Centered Design (UCD) recommends early and ongoing iterations with users

To optimize the design process we should attain as high degree of usability as we can on our first design cycle

Usability principles can help us achieve such a high degree of usability early in the design

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Usability and Product Success

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MS BOB Renault 4 circa 1970

Users rejected anthropomorphisms Negative transfer of training resulting in many errors

• Ignoring usability can impact the bottom line and safety

Quality of the Interaction - Usability

Efficiency Effectiveness Acceptance

Learnability Error/Safety Satisfaction

PerformanceSpeed Memorability Task completion

Usability of anapplication

UsabilityIndicators

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Effective interaction is determined by the goodness of fit between interface design and operator’s characteristics, needs, task requirements

Martijn van Welie (2001)

What is a UI Design PrincipleKnowledge gained from past design experience

and usability studies It’s a guide post pointing the way to a usable

designIt is not by itself an end or a ruleOne should try and follow it when it makes

sense, and deviate from it when needed

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UI Design Principles

Know your userLet the user control

the interactionCapitalize on what the

user already knowsMaintain consistency

at the interfaceProvide effective

feedback

Expose the interaction to the user

Minimize reliance on user memory

Minimize the impact of user error

Aesthetic mattersAlways test your

interface with users

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1) Know Your User – S/he is not you

Effective user interface is one that is compatible with and focuses on the users and their tasks. It considers:General human characteristics Characteristics the users of your application

Domain specific vocabularyComputer literacyGeneral education

Task specific characteristics of your usersTouch typistsFrequency of task performance

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Self Check-In Kiosk

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Designed for the general traveling population – What can you assume about the users of this system?

2) Let the User Control the Interaction

People want to control their environmentSoftware applications should be designed to

support the users, their task, and their interaction style

Constraining users’ action is fineControlling users’ action should be avoidedControllability can impact user satisfaction

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Ways to Increase User ControlLimit the extent to which users are forced to

perform a task in a predetermined wayMinimize the use of ModesAlways allow users to cancel outAllow users to save partial work such as forms

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3) Capitalize on what Users KnowUsing metaphors or familiar idioms (cut &

paste) at the interface will enable users to instantly understand the details of the application

Reusing knowledge will significantly enhance learning or reduce the amount of learning needed to achieve proficiency

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Using Metaphor– CD Control

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Using Metaphor - PIM

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4) Maintain ConsistencyConsistency enables users to anticipate events

and reuse learned behaviors -Positive TransferIt is achieved by reusing UI design structures

within and between applicationsComplying with standards for example

Reuse of knowledge reduces learning and enhances performance

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Consistent Menu and Tool Bars

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Consistency is not Always Good

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Usability is maximized by reusing usable elements – Duplicating bad design will result in a consistently bad designThis is a poor design for water temperature control and rinsing soapy hands

When Inconsistency is Good Inconsistent structure or design can be used to

attract user attention and prevent an automated response e.g., The delete dialog box

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5) Provide Effective Feedback

Feedback closes the action loop and “enables” the user to continue with his/her task or sequence of actions

Effective feedback is feedback that is provided to users: Immediately following the user’s actionAt an appropriate level

E.g., Action, Context, System state levelAt an appropriate place

E.g., at the locus of attention

Feedback improves performance and learning

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Effective Feedback

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6) “Expose” the Interaction to the User

Let the user see clearly the functions that are available at the interface

Exposing the interaction facilitates learning and performance

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Poor Visibility

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7) Minimize Reliance on MemoryAbility of users to recall commands, object

names, sequence of actions, etc. is limitedMake the interface visual with limited reliance

on recallAllow selection rather than relying on users to

remember a command or object nameExceeding memory limits hinders performance-

errors and speed

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Supporting Memory Limitation

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One way of supporting memory limitation is to use name recognition

Supporting Memory Limitation

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A better way of supporting memory limitation is to capitalize on both name recognition and visual recognition

Supporting Memory Limitation

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Another way of supporting memory limitation with both name recognition and visual recognition

8) Minimize the Impact of ErrorCost of errors impacts user performance

We are all afraid to err or loose our workWhen possible enable users to reverse their

actions Undo Confirm delete

Else, limit the cost of error Auto Save

But don’t over protect the userEasy recovery from errors enhances user

satisfaction and performance

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9) Aesthetics MatterConsider function first, form later

But don’t ignore form

Form or presentation often sets the moods of the user which in turns impacts users’ experience

Form or presentation facilitates: Visual scanning of a dialog box, window, page Location or detection of objects

Aesthetics enhances user satisfaction and performance

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Poor Aesthetics

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Poor alignmentInconsistent use of colorsAlso poor task flow

Use Colors carefully Use of color to convey information in the interface

should be accompanied with clear secondary cues

If red vs. green is the only way to tell which section is within bounds, about 6% of all users will have trouble telling the difference (9% Male, 2% Female)

Everyone is colorblind in low light

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10) Always Test Your InterfaceWe don’t have strong models of the human

operator/userWe can not predict (but can anticipate) how

certain design attributes will effect performance or satisfaction

We use testing to assess and refine our designs

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Lecture’s Main PointsEffective interaction design is built on

understanding how human act and the factors that impact human activity within a given context

Many of these factors have been captured by UI design principles

Adhering to these design principles will significantly enhance the usability of an interface

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