User Characteristics & Design Principles

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Lecture # 10

Objective of this lecture

Describe a set of important UI design principles Place these principles within the context of human

characteristics and show how they contribute to usability

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Achieving Usability

A key approach to achieving good usability is to continuously iterate our design with users But iterations consume resources

To minimize the number of iterations we capitalize on our collective past experience to create as usable design as we can already on our first design cycle

Usability principles are our collective past experience and can help us maximize usability early in the design

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Usability and Product Success

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pitz

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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 user’s characteristics, needs, task requirements

Martijn van Welie (2001)

What is a UI Design Principle

Knowledge gained from past design experience and usability studies about how to impact the usability indicators

It’s a guide post pointing the way to a usable design It is not by itself an end or a rule One should try and follow it when it makes sense, and

deviate from it when needed

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UI Design Principles

Know your user Let the user control

the interaction Capitalize on what the

user already knows Maintain consistency

at the interface Provide effective

feedback

Expose the interaction to the user

Minimize reliance on user memory

Minimize the impact of user error

Aesthetic matters Always 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 of our application’s users

Domain specific vocabulary Computer literacy General education

Task specific characteristics of your users Touch typists Frequency of task performance

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Self Check-In KioskGabriel Spitz

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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 environment Software applications should be designed to support

the users, their task, and their interaction style Constraining users’ action is fine Controlling users’ action should be avoided Controllability can impact user satisfaction

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Ways to Increase User Control

Don’t force users to perform a task in a predetermined way Allow Select & than create an account or vice versa

Always allow users to change their mind cancel out Allow users to save partial work such as forms

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3) Capitalize on what Users Know

Using metaphors or familiar idioms (cut & paste) at the interface will enable users to instantly understand the details of the application

Reusing knowledge will significantly 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 Consistency

Consistency enables users to anticipate events and reuse learned behaviors -Positive Transfer

It is achieved by reusing UI design patterns within and between applications Complying with standards or guidelines 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 pattern 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 their action At an appropriate level

E.g., Action, Context, System state level At 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

Recall the action Model by D. Norman

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Poor Visibility

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7) Minimize Reliance on Memory

Ability of users to recall commands, object names, sequence of actions, etc. is limited

Make the interface visual with limited reliance on recall Allow selection rather than relying on users to

remember a command or object name Exceeding 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 Error

Cost of errors impacts user performance We are all afraid to err or loose our work

When possible enable users to reverse their actions Undo Confirm delete

Else, limit the cost of error Auto Save

But don’t over protect the user Easy recovery from errors enhances user satisfaction and

performance

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9) Aesthetics Matter

Consider 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 Interface

We don’t have strong models of the human operator/user

We 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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Main Points

Effective 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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