Usability evaluations (part 3)


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Week 9 lecture for im2044 2012-2013

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Usability evaluations (part 3)

  1. 1. IM2044 – Week 9: Lecture Dr. Andres Baravalle 1
  2. 2. Outline • Design rules: principles, standards and guidelines • Usability inspections
  3. 3. Design rules: principles, standards and guidelines • Design rules are mechanism to restrict the domain of design options – Usability-related principles, standards and guidelines support the developer • Principles – General understanding of design as a subject area • Standards and guidelines – Direction for design • Design patterns – Capture and reuse design knowledge
  4. 4. Types of design rules • Principles • Standards – Specific design rules – High authority – Limited application increasing generality – Abstract design rules – Low authority – High generality increasing generality • Design rules differ in generality and authority G uide line s increasing authority S ta nda rds • Heuristics and guidelines – Lower authority – More general application increasing authority
  5. 5. Design principles 5
  6. 6. Principles to support usability • Learnability – The ease with which new users can begin effective interaction and achieve maximal performance • Flexibility – The multiplicity of ways the user and system exchange information • Robustness – The level of support provided the user in determining successful achievement and assessment of goaldirected behaviour
  7. 7. Principles of learnability • Predictability – Determining effect of future actions based on past interaction history • Synthesizability – Assessing the effect of past actions – Immediate vs. eventual honesty
  8. 8. Principles of learnability (2) • Familiarity – How prior knowledge applies to new system • Generalizability – Extending specific interaction knowledge to new situations • Consistency – Likeness in input/output behaviour arising from similar situations or task objectives
  9. 9. Principles of flexibility • Dialogue initiative – Freedom from system imposed constraints on input dialogue • Multithreading – Ability of system to support user interaction for more than one task at a time – Concurrent vs. interleaving; multimodality • Task migrability – Passing responsibility for task execution between user and system
  10. 10. Principles of flexibility (2) • Substitutivity – Allowing equivalent values of input and output to be substituted for each other (e.g. text and audio) – Representation multiplicity • Customizability – Modifiability of the user interface by user (adaptability) or system (adaptativity)
  11. 11. Principles of robustness • Observability – Ability of user to evaluate the internal state of the system from its perceivable representation • Recoverability – Ability of user to take corrective action once an error has been recognized – Reachability; forward/backward recovery; commensurate effort
  12. 12. Principles of robustness (2) • Responsiveness – How the user perceives the rate of communication with the system • Task conformance – Degree to which system services support all of the user's tasks – Task completeness; task adequacy
  13. 13. Design standards, guidelines and heuristics 13
  14. 14. Standards • Set by national or international bodies to ensure compliance by a large community of designers standards require sound underlying theory and slowly changing technology • Examples include: – W3C HTML and CSS standards – ISO 6385:2004: Ergonomic principles in the design of work systems
  15. 15. Guidelines and heuristics • Guidelines are detailed rules for design, often platform or task-specific • (Usability) heuristics are principles and rules of thumb that govern the overall design approach – Many textbooks and reports full of guidelines and heuristics – Understanding justification for guidelines aids in resolving conflicts
  16. 16. Usability inspections • Usability inspection methods are based on having evaluators inspecting an user interface • Usability inspection methods aim to examine usability-related aspects of an user interface, even if the interface has not been yet developed – Can be used to perform usability evaluations in the initial stages of the development 16
  17. 17. Usability inspections (2) • Heuristic evaluation and walkthroughs are the most common usability inspection methods 17
  18. 18. Heuristic evaluations • Heuristic evaluation is a method that requires some usability specialists to judge whether each element of an user interface follows established usability principles and guidelines – E.g. Jakob Nielsen’s heuristics • Heuristics being developed for mobile devices, wearables, virtual worlds, etc. 18
  19. 19. Heuristic evaluations: stages • Briefing session to tell experts what to do. • Evaluation period of 1-2 hours in which: – Each expert works separately – Take one pass to get a feel for the product – Take a second pass to focus on specific features • Debriefing session in which experts work together to prioritize and categorise the problems 19
  20. 20. Nielsen’s heuristics • Developed by Jacob Nielsen in the early 1990s. – Based on heuristics distilled from an empirical analysis of 249 usability problems. – These heuristics have been revised for current technology – and we will discuss them more in depth in the tutorial 20
  21. 21. Nielsen’s heuristics: discount evaluations • An heuristic evaluation is referred to as discount evaluation when 5 evaluators are used – Empirical evidence suggests that on average 5 evaluators identify 75-80% of usability problems on generalist web sites 21
  22. 22. Heuristic evaluations: advantages and problems • Few ethical & practical issues to consider because users not involved – Can be difficult & expensive to find experts – Experts should have knowledge of application domain & of the evaluation method used • Critical points: – Important problems may get missed – Focus can be lost on trivial problems – Experts have biases 22
  23. 23. Cognitive walkthroughs • Focus on ease of learning • Designer presents an aspect of the design & usage scenarios • Expert is told the assumptions about user population, context of use, task details. • One or more experts walk through the design prototype with the scenario. • Experts are guided by 3 questions 23
  24. 24. The 3 questions • Will the correct action be sufficiently evident to the user? • Will the user notice that the correct action is available? • Will the user associate and interpret the response from the action correctly? As the experts work through the scenario they note problems. 24
  25. 25. Pluralistic walkthrough • Variation on the cognitive walkthrough theme. – Performed by a team • The panel of experts begins by working separately • Then there is managed discussion that leads to agreed decisions. • The approach lends itself well to participatory design 25
  26. 26. Feature inspection • Feature inspection is a technique that focuses on the features of a product or of a web site – A group of inspectors that are given some use cases and are asked to analyse each feature of the web site for what regards availability, understandability, and other aspects of usability – This technique is better in the middle stages of development, when features are known but the artefact cannot be evaluated with methods as lab experiments. 26
  27. 27. Standards inspection • Standards inspection is a technique used to ensure the compliance of a web site against some standard • A usability professional with extensive knowledge of the relevant standards inspects a web site for compliance • Different standard inspections can be run on the same artefact – Nielsen’s heuristics include standards inspection 27
  28. 28. And now… • You have had an overview of a wide selection of usability evaluation methods – And you are ready to use them in your assignment 28