Presentation Transcript

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 “usability” of a system - no universal definition of the term Usability 2004 J T Burns

4. Usability Shackle LEAF • specifications take the form of precise statements of performance goals. • Typically related to • Ease of learning (Learnability) • Throughput (Efficiency) • Subjective matters of user satisfaction (Attitude) • Flexibility Usability 2004 J T Burns

5. Usability goals • Effective to use • Efficient to use • Safe to use • Have good utility • Easy to learn • Easy to remember how to use Usability 2004 J T Burns

6. 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? Usability 2004 J T Burns

7. User experience goals • Satisfying - rewarding • Fun - support creativity • Enjoyable - emotionally fulfilling • Entertaining …and more • Helpful • Motivating • Aesthetically pleasing • Motivating Usability 2004 J T Burns

8. 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? Usability 2004 J T Burns

9. Usability Evaluation Techniques • There are 4 core evaluation paradigms • Quick and Dirty • Usability Testing • Field Studies • Heuristic or predictive evaluation Usability 2004 J T Burns

10. 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 Usability 2004 J T Burns

11. 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 Usability 2004 J T Burns

12. 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 Usability 2004 J T Burns

13. 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 Usability 2004 J T Burns

14. 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 Usability 2004 J T Burns

15. 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...” Usability 2004 J T Burns

16. 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 Usability 2004 J T Burns

17. 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 Usability 2004 J T Burns

18. Components of a usability specification • Statement of the usability goal • Statement of the usability attribute • Statement of the criteria which will represent attainment of the specification • Now level • Worst case • Planned level • Best case • Statement of which set or subset of users the specification applies to • A statement of preconditions for the measurement Usability 2004 J T Burns

19. 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 2004 J T Burns

20. Usability Specification • Provide an alternative usability specification using a different attribute that could determine whether the stated goal had been achieved Usability 2004 J T Burns

21. 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 Usability 2004 J T Burns

22. 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 2004 J T Burns

23. Further Reading • www.useit.com • This is the usability site of Jacob Nielsen Usability 2004 J T Burns