Usability evaluations (part 3)

IM2044 – Week 9: LectureDr. Andres Baravalle

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Outline

• Design rules: principles, standards and guidelines

• Usability inspections

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

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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Standards

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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

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

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

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

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)

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

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

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

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

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

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

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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