principles of user centred design howell istance

Principles of User Centred Design

Howell Istance

Some definitions

Human-Computer Interaction a discipline concerned with the design, evaluation

and implementation of interactive computing systems for human use and with the study of the major phenomena surrounding them

User Interface any boundary between the human user and the

computer system (includes documentation and training material)

not restricted to screens, keyboards and mice

User Centered Design

all systems need not be designed to suit everyone...

.... but should be designed around the needs and capabilities of those people who will use them

usability - concerned with making systems easy to learn, easy to use and efficient to use

Think about a car... how much knowledge about a car do you to be able to

drive it? do the best designed cars give the driver the most

information about the engine, suspension, etc? good design of the interface to the car includes designing

controls that are obvious to use behave in the way you expect give fast feedback are comfortable to use hide unnecessary information from the user

Misconceptions about user interface design a usable system has lots of

functions ‘I know it’s a bit hard to use but it’s

all described in the Help system’ ‘I know it works - I’ve got the

people in the office (or on the course) to use it’

Visibility, mapping and affordance

visibility: the correct parts must be visible, they must convey the correct message - that message is conveyed by signals

mapping: the relationship between what you want to do and what appears to be possible - good design exploits natural and easily perceived mappings

affordance: the perceived and actual properties of a thing, primarily those fundamental properties that determine just how the thing could possibly be used

Perspectives on design

think ‘design first, implementation second’ design the interface first for usability, only

compromise in the design for ease of implementation later if necessary

think how the system and interface should support what the user wants to do, rather than what the system is capable of doing

Implications for the design process

early focus on users and tasks clear understanding of what particular usability

attributes are important testing of prototypes of the design from an early

stage in the process results from prototype testing need to be used to

modify the design, which is retested software tools are needed to support this process - to

enable designs to be built and modified with little programming overhead

Waterfall model of S/W development

certainly better than no model at all, but too rigid requirements change during design process testing occurs late in the process

requirements analysis & definition

System and software design

implementation and unit testing

integration and system testing

operation & maintenance

Prototyping Model of S/W development

requirements definition

quick design

build prototype

evaluate and refine requirements

engineer product

Prototyping Model of S/W development

Advantages evaluation at an early stage prototype can be used to explore further

requirements

Disadvantages quick design may be badly founded building prototypes may not necessarily be rapid

Components in a user centred design

Product requirements (including usability specification)

Usability Specifications

Usability - extent to which application is easy to learn, easy to use and efficient to use

specification - defining what constitutes success in terms of measurable quantities

e.g ‘90 % of first-time users (without prior training) will be able to retrieve the shelf number of a given book within 300% of the time it would take an expert user to do so’(possible example from a library information system)

Knowledge of users

- general psychology

-characteristics of user groups


Users

Subject of next lecture

Knowledge of users



Knowledge of users’ tasks and information requirements


Tasks

Task Analysis involves study of the work users do, the component tasks within this and the information needed to complete each task

Object of interface design is to fit the design (content, navigation) around these task needs

Several different methods of capturing this Important to represent the analysis so that its

correctness maybe checked with groups of users

Knowledge of users




Knowledge of environment in which application will be used


Environment

In general terms this refers to the physical and organisational environment

physical - location (e.g home, railway station, public libray) and the constraints this places on design solutions

organisational - usually an issue when introducing systems into businesses - systems need to fit the way in which they will be used

Knowledge of users






Knowledge of design principles - HCI, graphics, typography

Design principles Important to know what design guidance is available

and use what is already known design can not proceed by recipe, principles of good

practice can be given to the designer who needs to apply these HCI principles - quality of user-computer dialogue Graphics Design - means of effective and aesthetic

visual communication Typography - effective and aesthetic use of style in

text

Knowledge of users







Knowledge of delivery platform and I/O devices

Knowledge of users








Produce prototype

Prototypes

Early prototypes usually paper-based, used to quickly capture ideas

Later prototypes built on a machine to give a realistic ‘mock-up’ of what the final application will look like Should have sufficient functionality to enable

interactive testing before final version is available

Knowledge of users








Produce prototype

Evaluate prototype though structured testing

Evaluation

‘expert’ based appraisal based on walk-throughs of the design in the context of completing selected tasks

subject based testing where people representative of the user population are observed completing selected tasks with the prototype

emphasis as much on qualitative data as on quantitative data

principles of user centred design howell istance

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