usability dss

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Management Information SystemsManagement Information Systems

Usability & Cognitive Engineering

Jerry Fjermestad

Copyright 1998-1999

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The design principles for The design principles for usability (Gould & Lewis, 1985)usability (Gould & Lewis, 1985)

1. Early focus on the users 2. Empirical measurement 3. Iterative design 4. Integrative design (help, training, documentation,

etc in parallel).

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UsabilityUsability

1. Early focus on users bring the design team into direct contact with the

users right from the start get the user involved so they can instill their

knowledge into the design process

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UsabilityUsability

2. Empirical measurement actual behavioral measures of

– learnability– usability

testing of appropriate task or concepts memory access speeds, time to learn the function keys remember novices are different form experts.

collect the user thoughts (use protocol analysis) collect the user's mistakes collect the user's attitudes

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UsabilityUsability

3. Iterative design incorporate the results from the tests into the next

prototype set goals for the system an evaluation criteria

– easy to use– user friendly– easy to operate– simple– responsive– flexible

this is feedback and evaluation

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UsabilityUsability

4. Integrated design build help, training, documentation, process modules

at the same time.

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Usability DefinitionsUsability Definitions

Usability is task related, people related and function related. It has cognitive, behavioral, and communicative components.

To be truly usable a system must be compatible not only with the characteristics of human perception and action but, and most critically, with user's cognitive skills in communication, understanding, memory and problem solving." (Hammond, 1981)

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Usability DefinitionsUsability Definitions

Designing a usable system requires: understanding of the intended users. the amount of time they expect to use the

system. how their needs change as they gain

experience. (Goodwin, 1987)

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Usability DesignUsability Design

1. Early focus on the user What: understand the user's cognitive, behavioral,

attitudinal - and goals of the organization How: interviews, observations, discussions, working

with the users. 2. Empirical Measurement

What: Tasks and dependent measures. How: Testing - protocol analysis, observation,

interviews, etc.

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Usability DesignUsability Design

3. Interative design What: The problems encountered are to be corrected

and measure again. How: An evolving system - prototyping.

4. Integrated Design What: a parallel development of interface, help,

documentation, training and measurement.

Gould & Lewis, 1985, Gould, et al. 1991

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Measurable HumanMeasurable HumanFactors Goals (Usability)Factors Goals (Usability)

Time to learn - How long does it take for typical members of the target community to learn to use the commands relevant to a set of tasks?

Speed of performance - How long does it take to carry out the bench set of tasks?

Rate of errors by users - how many and what kinds of errors are made in carrying out the benchmark set of tasks?

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Measurable HumanMeasurable HumanFactors Goals (Usability)Factors Goals (Usability)

Subjective satisfaction - How much did the users like using aspects of the system?

Retention over time - How well do users maintain their knowledge?

Shneiderman, B., Designing the User Interface, 14

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Cognitive EngineeringCognitive Engineering

Learning is a relatively permanent change in behavior resulting from conditions of practice

Human learning then is the association of one item with another item, paired associated learning

pairs of stimuli come in, a mental association is made for them, and the stimuli then become interrelated

Future learning can then depend upon past learning. People develop new cognitive structures by using

metaphors to cognitive structures they have already learned

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The metaphor is a model or structure or conceptual framework which help bridge any gap between what the person (user) knows and what is being attempted to be learned.

metaphors spontaneously generated by users will predict the ease with which they an master a computer system

If this is indeed the case then systems designers must understand and employ the use of metaphors in system designs

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Carroll and Thomas (1982) developed eight recommendations to aid both the user and designer in build effective systems 1. Find and use appropriate metaphors in teaching

the naive user a computer system. A metaphor to be useful must have a suitable domain for a given system and given user population.

2. Given a choice between two metaphors chose the one which is most congruent with the way the system works.

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3. Assure that the correct attitude is presented. Costs of ignoring this recommendation range from user dissatisfaction and reduced productivity to sabotage.

4. When more than one metaphor is need to represent a system, choose metaphors that are similar enough, but not to similar that confusion results.

5. Consider the probable consequences to users and system designers of each metaphor used. This is the evolving state from novice to user. Two path are possible: one leading to directly to the system, the other to a new metaphor.

6. The limits of the metaphor should be pointed out to the user.


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7. The intent of the metaphor in the beginning is to aid understanding and usability; for the continual user, it is no longer necessary. The metaphor is used also as a motivator, at first to get the user to use the system, then to make him productive and keep his interest.

8. Provide the user with an exciting metaphor for routine work and eventually present the user with advanced scenarios requiring different action.

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Learning is a relatively permanent change in behavior resulting from: Elaboration, association, practice, rehearsal.

Metaphor - a mental model, structure, or framework which help bridge any gap between what a person knows and what is being attempted to be learned.

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Cognitive EngineeringCognitive Engineering(goals)(goals)

To understand the fundamental principles of human action and performance relevant to the principles of system design.

To devise physical systems that are pleasant to use.

Psychological variables - goals, intentions and attitudes

Physical variables - pertain to to system.

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Human-Computer DialogueHuman-Computer Dialogue

computer based systems should be easy to learn and remember, effective, and pleasant to use.

these are testable usability behavioral measures that are consisted with what Gould and Lewis (1985) have suggested.

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Molich and Nielsen (1990) nine basic categories of usability problems:

– 1. Simple and Natural Dialogue: The dialogue should be simple and clearly stated. It should not contain any irrelevant information. The information should appear in a natural and logical order.

– 2. Speak the User's language: The dialogue should be expressed in the terminology familiar to the user rather than in system oriented terms.

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– 3. Minimize the User's Memory Load: Instructions should be visible, easily retrievable, and simplified. Information presentation load should be reduced when ever possible (i.e., users should not have to remember file names when they are retrievable).

– 4. Be Consistent: The terminology and concepts should always be used in the same manor.

– 5. Provide Feedback: The system should provide feedback as to what is transpiring within a reasonable time.

– 6. Provide Clearly Marked Exits: Clearly marked exists should be provided to the user in case of mistakes.

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– 7. Provide Shortcuts: System flexibility for the novice and expert. Menus for the novice and commands for the experts.

– 8. Provide Good Error Messages: The error messages should be constructive and provide meaningful suggestions to the user of what to do next.

– 9. Error Prevention: A careful design that prevents error messages form occurring in the first place.

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Conclusion:– the identification of specific, and potential usability

problems in a human computer dialogue design is difficult.

– usability goals be defined and incorporated into the design.

– designers may have difficulties in applying the principles of Gould and Lewis (1985) unless they have simple basic requirements for the design product

– This statement draws attention to the first principle from Gould and Lewis (1985), early focuses on the user

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– In this respect the design team defines the application and measures of usability

– The nine principles were derived from experience and then analyzed a posterior from a survey.

– these nine measures are analyzed for graphical interface designs and are even more important since graphical interfaces increase the degrees of freedom by orders of magnitude.

– also suggests that no single interface principle can be absolute, there is a need for trade-offs.

– the user team define what is need, let the system evolve and measure usability.

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– The major differences between Molich and Nielsen (1990), and Gould and Lewis (1985) are three fold.

– 1. Gould and Lewis are defining usability as a set of rules an principles which are subject to the needs of the user and the tasks; the usability measures are defined in this context and; there is an iterative cycle for development.

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– 2. Molich and Nielsen (1990) and Nielsen (1990) are applying the usability measures to systems that are not in the design phase (a posterior analysis).

– 3. Gould and Lewis are a priori.

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Summary: The objective of the metaphor is to add psychology

to the user interface In designing a human computer interface the

designer must implicitly build in a psychological (mental or cognitive) model of the system

The usability of the system then depends upon the users mental model and the designers projection of what the users mental model should be

The smaller the distance the greater the usability.

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Summary (con’t) usability is the distance between the design model

and mental model, the smaller the distance the greater the usability

The interface is what bridges the gap, the more it responds the way the user' mental picture says it should, the more usable it is.

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Gulf of Execution

of Execution

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GulfsGulfs Gulf of Execution: Bridged by

Psychological Metaphor, intentions, practice

Physical The interface design

Gulf of Evaluation: Bridged by Psychological

Comparisons between goals and expectations (formed attitudes, cognitive dissonance)

Physical proper output interface

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Brown and Newman (1985) have suggested that are five main issues to understanding system usability: 1. System opacity- Computer based systems are

opaque, there function can not be perceived from their structure.

2. System complexity- Computer based system allows the users to access and manipulate many processes simultaneously.

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3. Social complexities- Differences in perceived values and styles brought about either though cultural or individual expectations.

4. Lack of appropriate metaphor- An inappropriate model of the system either mental (user) or design.

5. Interactivity and ambiguity- The goals, intention or purpose of the system, interface, or output not defined clearly.

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Brown and Newman (1985) recommend an integrative approach used to design used to implement computer based systems

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Brown and Newman (1985) recommend an integrative approach (con’t) This approach includes:

– 1. the development of mental models and metaphors to aid in understanding.

– 2. communicative repair which is used in iterative testing and modification.

– 3. training strategies which is an integrated parallel approach.

– 4.setting the organization goal and objectives which is the early focus on the user.

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Cognitive definitionsCognitive definitions

Usability is the distance between the design model and mental model, the smaller the distance the greater the usability.

How?

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Cognitive definitionsCognitive definitions

Brown & Newman(1985)

Gould & Lewis (1985)

Develop mental models Early focus on usersCommunicate Iterative testingMeasure MeasurementSet goals & objectives Integrative

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