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Specific
antecedent
Determine
error mode
(general
consequent)
Description
of initiating
event
(e.g., accident)
No general
antecedent
Analysis
complete
Add specific
consequent
General
antecedent
Yes
Match with
general
consequent
Any
match?
No
Fig. 10.5
CREAM. The basic CREAM analysis process (redrawn by the authors)
process, although the iterations take place at a higher level, i.e., the level of the
design of the system or device.
The THEA process (see Fig.
10.6
) starts with a description of the system in
terms of its functional behavior, its interface, and how it communicates with other
systems. This description is accompanied by a corresponding description of the
work performed by the system. This comprises one (or more) descriptive sce-
narios, particularly focusing on the potential vulnerabilities of the system, and a
description of the sorts of tasks that will be performed in terms of goals, actions,
and plans.
The system description and work descriptions are used to structure the scenario.
Any appropriate method that can be used to decompose goals, such as hierarchical
Once you have a structured scenario, you can do the error analysis. The analysis
is based on a set of questions and a model of human information processing.
Although the THEA reference guide uses Norman's (
1988
/
2013
) cyclic model of
interaction, the process is model independent.
The final step is to consider the probability of the occurrence of the identified
errors, and then make suggestions about changes to the design to deal with them.
The process then iterates until some stopping point is determined, which will
usually be down to the judgment of the designer.
As with the CREAM, THEA's uptake has been somewhat limited but, like the
CREAM, it also shows how a systematic approach to analyzing errors can be used
to inform design. Those who want more information should consult the THEA
reference guide. THEA was originally designed to analyze situations involving a
single person using a single artifact, whereas nowadays most work is performed by
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