Usability 2004 J T Burns1 Usability & Usability Engineering.

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Usability 2004 J T Burns 1 Usability & Usability Engineering
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Transcript of Usability 2004 J T Burns1 Usability & Usability Engineering.

Usability 2004 J T Burns 1

Usability & Usability Engineering

Usability 2004 J T Burns 2

Usability What is usability Easy to use? User Friendly? A system with a GUI?

Usability 2004 J T Burns 3

Usability Engineering

No clear definition until fairly recently First proposed by Shakel 1987 Tried to provide an operational

definition of Usability quantify the “usabilityusability” of a system - no

universal definition of the term

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Usability Shackle

LEAF specifications take the form of precise

statements of performanceperformance goals. Typically related to

Ease of learning (LearnabilityLearnability) ThroughputThroughput (Efficiency) SubjectiveSubjective matters of user satisfaction (Attitude) Flexibility

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Usability goals Effective to use Efficient to use Safe to use Have good utility Easy to learn Easy to remember how to use

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Activity on usability How long should it take and how

long does it actually take to: use a VCR to play a video? use a VCR to pre-record two

programs? use an authoring tool to create a

website?

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User experience goals Satisfying - rewarding Fun - support creativity Enjoyable - emotionally fulfilling Entertaining …and more Helpful Motivating Aesthetically pleasing Motivating

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Usability and user experience goals How do usability goals differ from

user experience goals? Are there trade-offs between the

two kinds of goals? e.g. can a product be both fun and

safe? How easy is it to measure usability

versus user experience goals?

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Usability Evaluation Techniques

There are 4 core evaluation paradigms

Quick and Dirty Usability Testing Field Studies Heuristic or predictive evaluation

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Quick and Dirty Is common practice where designers get

feedback from users or HCI consultants to check there ideas are ok

Can be done at any stage – emphasis is on speed rather than detailed well documented findings – do you like this layout, this icon?

Is used when timescales are short Has become particularly popular in web

design

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Usability testing Dominant approach in 80’s remains

very important – typically lab based Move towards other forms including

field testing and heuristic evaluations Testing involves measuring typical

users performing real tasks and recording the time taken or number of errors made

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Usability – Field Tests Field studies of usability are done in the

users natural setting Aims to determine what the user

actually does and what other elements may impact on the interaction with the device or system

Field studies can be used to Identify opportunities for new products Determine requirements for design

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Usability testing Recording of users performance may be

through a number of techniques including Video recording Direct observation Software logging

Resulting data is used to inform the design and engineer it to meet the desired performance levels – usability engineering

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Usability principles/heuristics Similar to design principles, except

more prescriptive Used mainly as the basis for

evaluating systems Provide a framework for heuristic

evaluation Experts guided by heuristics to

predict usability problems

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Usability specifications

Whiteside et al proposed that usability could be measured in terms of attributes which can be measured

Important because they offer a way of incorporating usability into software quality assurance specifications

Example (of a data retrieval system) “90% of all users will be able to

identify the location of a book in the library by its shelf number, given the author’s name and book title, within ten seconds...”

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Objective of usability specifications To make decisions about user interface goals

explicit Support effective collaboration within the design

team, between its members Usability specification becomes part of the

general requirements specification Is an essential and integral part of UCD

Can be used to resolve conflict between,for example, users, analysts and designers over parts of the design

Can help determine whether need for further iterations and prototyping

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Usability Attributes Attributes should be measurable Example Attributes include

Time to complete a task % of task completed Number or % of errors made % of users who like the design No of times user asks for help/gets lost

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Components of a usability specification

Statement of the usability goal Statement of the usability attributeusability attribute Statement of the criteriacriteria which will represent

attainment of the specification Now level Worst case Planned level Best case

Statement of which set or subset of usersusers the specification applies to

A statement of preconditionspreconditions for the measurement

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Sample specification

Usability Goal: Users can quickly obtain a balance from an ATM Attribute: Time Measuring method: Observe and record

Time taken by users to obtain balance Now level: 30 secs Worst case: 25 secs Planned level: 20 secs Best case: 15 User class: All Preconditions: Users are familiar with ATMs

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Usability Specification Provide an alternative usability

specification using a different attribute that could determine whether the stated goal had been achieved

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Usability principles (Nielsen 2001)

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

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Problems with UE Assertion of clear measurable criteria Measures specific user actions in

specific situations Other factors may contribute to overall

performance Setting appropriate criteria

Important to look for ‘now’ level

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Further Reading www.useit.com

This is the usability site of Jacob Nielsen