usability 2009 j t burns1 usability & usability engineering

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  • Slide 1
  • Usability 2009 J T Burns1 Usability & Usability Engineering
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  • Usability 2009 J T Burns2 Usability What is usability Easy to use? User Friendly? A system with a GUI?
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  • How do we build bridges? How do we build skyscrappers? Usability 2009 J T Burns3
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  • 4 Usability Engineering No clear definition until fairly recently First proposed by Shakel 1987 Tried to provide an operational definition of Usability usability quantify the usability of a system - no universal definition of the term
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  • Usability 2009 J T Burns5 Usability Shackle LEAF performance specifications take the form of precise statements of performance goals. Typically related to Learnability Ease of learning (Learnability) Throughput Throughput (Efficiency) Subjective Subjective matters of user satisfaction (Attitude) Flexibility
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  • Usability 2009 J T Burns6 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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  • Usability 2009 J T Burns7 Activity on usability How long should it take and how long does it actually take to: use a DVD to play a video? use a PVR to record two programs? use an authoring tool to create a website?
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  • Usability 2009 J T Burns8 User experience goals Satisfying- rewarding Fun- support creativity Enjoyable- emotionally fulfilling Entertainingand more Helpful Motivating Aesthetically pleasing Motivating
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  • Usability 2009 J T Burns9 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 2009 J T Burns10 Usability Evaluation Techniques There are 4 core evaluation paradigms Quick and Dirty Usability Testing Field Studies Heuristic or predictive evaluation
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  • Usability 2009 J T Burns11 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 2009 J T Burns12 Usability testing Dominant approach in 80s 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 2009 J T Burns13 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 2009 J T Burns14 How might you undertake an evaluation of a family using an innovative home entertainment system that gave them wi-fi access throughout the home with access to the internet, video on demand, PVR programming, games etc? What would you want to evaluate?
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  • Usability 2009 J T Burns15 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 2009 J T Burns16 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 2009 J T Burns17 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 authors name and book title, within ten seconds...
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  • Usability 2009 J T Burns18 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 2009 J T Burns19 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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  • Usability 2009 J T Burns20 Components of a usability specification Statement of the usability goal usability attribute Statement of the usability attribute criteria Statement of the criteria which will represent attainment of the specification Now level Worst case Planned level Best case users Statement of which set or subset of users the specification applies to preconditions A statement of preconditions for the measurement
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  • Usability 2009 J T Burns21 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 2009 J T Burns22 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 2009 J T Burns23 Usability Specifications Create a usability specification for the following devices/systems A web site selling books An MP3 player A airline reservation system A self service check in system
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  • Usability 2009 J T Burns24 Some attributes you may have thought of: No of clicks Time No of errors Time to learn % who remember functions/meaning of icons % Can use 1 st time
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  • Usability 2009 J T Burns25 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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  • Usability 2009 J T Burns26 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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  • Usability 2009 J T Burns27 Further Reading This is the usability site of Jacob Nielsen


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