Cost Effectiveness of Usability and Human Error
Abbas Moallem, Ph.D.
Outlines
Why Develop a User-Friendly Product?
Cost of Errors
Introduction Human Error in HCI
Classification of Human Error
Preventing Human Errors
Designing for Error Tolerances
Why Develop a User-Friendly Product?
The Palm Beach Country "Butterfly Ballot
Cost of Error
An error occurs once per week (0.2 per day).
This error delays user 2 minutes in performing a task. (0.4 minute per day)
Example Error Messages
Cost of Error
An error occur once per week (0.2 per day).
This error delays user 2 minutes in performing a task. (0.4 minute per day)
Benefits of Reducing Error
Evaluation of an interface to identify the error
20hr @ $120/hr = $2400
Programming cost to implement suggestions:
30hr @ $120/hr = $3600
Total Cost of DesignTotal cost of error
$6000 $191,666.000
Questions
What is error?
What is Error?
What is Mistake?
What is Slip?
Errors are attributable to individual.
Error reveals what a person was really thinking but did not whish to disclose.
Introduction
Error is Human.
If an error is possible, someone will make it. (Norman (1988)
Classifying Human Error
According the Webster's New World Dictionary “error" are:
the state of believing what is untrue, and
something incorrectly done
Researcher suggest two definitions of error by defining error as:
a divergence between the action actually performed and the action that should have been performed, or
an action or event
Classifying Human Error
Action sequence triggered by knowledge structures (organized as memory units and called schemas). The mind comprises a hierarchy of schema that are are invoked (or triggered) if particular condition satisfied or events occur. (Norman 1981)
Apply more to skilled behavior.
Classifying Human Error
Another method of error classification is developed by Reason incorporating slips, lapses, and mistakes.
Slips and lapses are defined by attentional failures and memory failures, respectively.
Both slips and lapses are examples of where the action was unintended, whereas mistakes are associated with intended action. (Reason 1990)
takes the information processing framework to consider the implication of psychological mechanisms in error formation.
With mistakes the situation assessment and/or planning are poor, whereas the retrieval action execution is good.
With slips, the action execution is poor, whereas the situation assessment and planning are good.
With lapses, the situation assessment and action execution are good, but memory is poor. (Wickens 1992)
Classifying Human Error
knowledge of how the world works (e.g., mental models) leads to the anticipation of certain kinds of information, which in turn directs behavior to seek out certain kinds of information and provide a ready means of interpretation.
During the course of events, as the environment is sampled, the information serves to up date and modify the internal, cognitive schema of the world that will again direct further search. (Neisser 1976)
Classifying Human Error
knowledge of how the world works (e.g., mental models) leads to the anticipation of certain kinds of information, which in turn directs behavior to seek out certain kinds of information and provide a ready means of interpretation. During the course of events, as the environment is sampled, the information serves to up date and modify the internal, cognitive schema of the world that will again direct further search. (Neisser 1976)
Classification of Human Error
Error Phenotypes: Observable State Undesirable
Error Genotype: Generative Mechanisms of Observable States
Classification of Human Error
Classification of Errors by their Consequences
Classification of Error by their Underling
Slips and Mistakes
Cognitive Control and Systemic Error
Errors Relating to Learning Adaptation
Errors due Interfaces among Competing Cognitive Control Structures
Errors due to Lack of Resources
Errors due to Intrinsic Human Variability
Error Shaping factors
Classification of Errors by their Consequences
Describe Superficial Nature of error
Example:
Omissions, Substitutions
Pressing “delete”instead of “end”
Analyze “How” the Error has Happen rather than “Why”
Classification of Error by their Underling Causes
Dissimilar Errors Forms may have Similar Causes
Analyze Cognitive base of Errors
Slips and Mistakes
Slips: Failure of Execution
Mistakes: Planning Failures (the action may go as planed but the plan itself is wrong)
How to reduce errors
Making the limit of acceptable performance visible to users, while the effects are still observable and reversible
Provide feedback on the effects of actions to allow the users to cope with the delay between the execution of an intention and the observation of its effects
Make overview displays available to avoid capture errors at the skill-based level
How to reduce Errors (Conti.)
Support memory with externalization of the effective mental models
Develop consistent information transformation concepts
Support of memory of items, acts , and data which are not part of an integrated : “gestalt” can be useful
Reduce Errors
Avoiding Mode Errors
Maintaining Consistency
Facilitating Multiple Activities
Reduce in Head Memorizing
Knowledge about Users
Understanding Cultural Issues
Providing Appropriate Metaphors and Icons
Using Colors
On Line Help & Training
More Information
The Design of Everyday Things, Norman, Donald A. Currency Doubleday, 1988, USA
The Handbook of Human –Computer Interactions, Chapter 22 page 489-501
Human Error, J. Reason, Cambridge University Press, UK, 1990
For More Information
Karat, C. (1997). Cost-justifying usability engineering in the software life cycle. In Helander, M., Landauer, T., and Prabhu, P. (Eds), Handbook of Human-Computer Interaction. Elsevier Science, Amsterdam. ·
Karat, C. (1990). Cost-benefit analysis of usability engineering techniques. Proceedings of the Human Factors Society. Orlando. Fl. ·
Norman, D. (1998). The Invisible Computer: Why Good Products Can Fail. MIT Press, MA. ·
Moore, G. (1991). Crossing the Chasm. Harper Business, NY.
Pressman, R.S. (1992). Software Engineering: A Practitioner's Approach. McGraw Hill, NY.
Schlesinger, L.A., and Heskett, J.L. (1991). A service driven service company. Harvard Business Review, 69, 5, 71-81.
Wildstrom, S. (1998). A computer user's manifesto. In Technology and You, Business Week, Sept. 28.
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COE296/AM/SCU/Session 4