Human Error Dr. Earl E. Hansen, CIE

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Human Error

. Earl E. Hansen, CIE

Human Error
Difficult to Discuss/Analyze

Relatively new field

Still trying to:

define its boundaries

define its terminology

define its taxonomy

Errors Happen

Seems trivial on the surface

No matter how good a system or
design is, people will make mistakes

some subscribe to the concept of “Normal Errors”
errors that are inevitable in
complex systems

Systems Can Encourage Errors

Errors are often attributed to the action of an individual
there are often a set of
forces & preceding events that lead up to the error.

These forces & events are difficult to anticipate.

Reaction is to punish individual and not to examine the system

Studying Human Error

Reinforces existing guidelines for good design.

Is the analysis o
f human performance.

Expects humans to make errors

Focus on error tolerance

Focus on error recovery

Focus on error prevention

New technologies will succeed or fail based on our ability to minimize the
incompatibilities between

the characteristics of peopl
e and

the characteristics of the things we create

Cognitive Science (Engineering)

A mix of different disciplines (psychology, philosophy, neuroscience, & artificial

Ergonomics/Human Factors

Reviews specifics of human performance & how it

can be improved.


Physical and Physiological.

Human Factors


What Is Human Error?

“Human error: an inappropriate action, or intention to act, given a goal and the
context in which one is trying to reach that goal.” Ramon
, 1995

A Theory of Cognition

Accidents typically occur due to mental error.

James Reason

There are three basic kinds of mechanisms of thought





The ability to carry out a task; skill

cognitive pr
ocessing and performance refers

actions that are automatic and easy to due

to an acquired skill. Example: getting out bed.

Putting on a T
shirt, or opening a door

all of

which are unconscious actions one doe not

need to explicitly “think about” to

omplish. Automatic which arm in what



Matching the context & problem currently

facing the actor. These rules are typically of

the “if X then Y” form, can be based on past

experience, explicit instructions, etc.

in leaving a room,
one normally

pushes the door to exit (automatic skill). If the

door does not open one start down a list of

reasons. Locked, pull, etc.


If rule
based processing does not solve the problem,

we fall back on knowledge
processing (tend to

prefer rule
based solutions since they require less

cognitive effort on
our part). Occurs when faced

with novel or unfamiliar situations, or where low

level rules
are not appropriate (e.g. making strategic

decisions, diagnosis, etc.) Involves processing

symbolic information (suits in card deck) reduces

cognitive effort. Cognitive
mechanisms are Slips &


Slips: Errors of Action

Action not in accord with ones intentions: a good plan but poor execution. i.e.
fumble on a good play. They are p
art automatic, unconscious actions, slips are
unintended acts due to a break in the routine.

Slip Error Mechanisms

Capture slips
doing something automatically one did not intend to do. Fell into a
pattern one performs frequently.

Description slips
to tell self correctly what one wants to do. Occurs when
intended action is similar to other actions done often.

Associative activation slips
occur when the brain makes a faulty connection or
mental association between tow ideas, often when one is an exter
nal stimulus that
typically provokes a certain action. e.g. answering phone when hearing the

Loss of Activation slips
occur when one loses track of what they are doing or
trying to do (the activation of the process). Essentially a temporary memor
y loss,
often due to interruption, asked a question, handed something. e.g. “now why did
I get up to come into this room in the first place?”


Errors of Intention


Stem from cognitive breakdowns; often influenced by external system
s. A planning failure, when actions go as planned
but the plan was bad.
These are errors of judgement, influence, etc., that result in an incorrect intention,
incorrect choice of criterion, or incorrect value judgement. Mistakes are the real
challenges i
n the analysis of human error. Slips can be prevented through checks
built into tools/equipment.

Based Errors

Occur when:

the wrong rule chosen due to misperception of the situation

misapplication of rule

Based Errors

The most complex of


Occurs from a lack of or misapplication of knowledge