Usability evaluations (part 3)

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Week 9 lecture for im2044 2012-2013

Text of Usability evaluations (part 3)

  • 1. IM2044 Week 9: Lecture Dr. Andres Baravalle1

2. Outline Design rules: principles, standards and guidelines Usability inspections 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. Types of design rules Principles Standards Specific design rules High authority Limited applicationincreasing generality Abstract design rules Low authority High generalityincreasing generality Design rules differ in generality and authorityG uide line sincreasing authority S ta nda rds Heuristics and guidelines Lower authority More general applicationincreasing authority 5. Design principles5 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. 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. 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. 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. 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. 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. 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. Design standards, guidelines and heuristics13 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. 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. 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. Usability inspections (2) Heuristic evaluation and walkthroughs are the most common usability inspection methods17 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 Nielsens heuristics Heuristics being developed for mobile devices, wearables, virtual worlds, etc. 18 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 problems19 20. Nielsens 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 tutorial20 21. Nielsens 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 sites21 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 biases22 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. 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. 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. 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. 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 Nielsens heuristics include standards inspection 27 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 assignment28