usability & usability engineering. usability what is usability easy to use? user friendly?
Post on 20-Dec-2015
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Usability & Usability Engineering
Usability What is usability Easy to use? User Friendly?
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
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
Usability specifications
Whiteside et al extended definition Measured usability 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...”
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
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
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
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
Usability Specification Provide an alternative specification
using a different attribute that could determine whether the stated goal had been achieved
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
Usability Some Questions What are the key factors for successful
usability work? Is usability recognised as an important
design issue? Are organisations designing for
usability?
Further Reading Preece Chpts 1, 6 & 7