Transcript
Page 1: Usability evaluations (part 3)

IM2044 – Week 9: LectureDr. Andres Baravalle

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Outline

• Design rules: principles, standards and guidelines

• Usability inspections

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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

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Types of design rules

• Design rules differ in generality and authority• Principles

– Abstract design rules

– Low authority

– High generality

• Standards– Specific design rules

– High authority

– Limited application

• Heuristics and guidelines– Lower authority

– More general applicationincreasing authority

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Design principles

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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 goal-directed behaviour

Andres Baravalle
e.g. Can the user understand wheter s/he managed to complete the task?
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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

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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

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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

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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)

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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

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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

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Design standards, guidelines and heuristics

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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

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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

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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

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Usability inspections (2)

• Heuristic evaluation and walkthroughs are the most common usability inspection methods

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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.

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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

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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

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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

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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

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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

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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.

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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

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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.

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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

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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

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