Human Error & Bias

Human Error and Biases
Human Error - Definition
An inappropriate or undesirable human
decision or behavior that reduces, or has the
potential for reducing, effectiveness, safety, or
system performance.
An undesirable effect or potential effect on
systems or people.
An error that is corrected before it can cause
damage is an error nonetheless.
Error Classification
Discrete Action
Omission - Forgetting to do something, or just
deliberately ignoring it.
Commission - Performing an act incorrectly.
Sequence - Right action, wrong order.
Timing / Rate -Too fast or too slow.
Error Classification
Information Processing
Specific error categories at each stage of
information processing.
1. Observation of system state
2. Choice of hypothesis
3. Testing of hypothesis
4. Choice of goal
5. Choice of procedure
6. Execution of procedure
Error Classification
Information Processing - continued
The errors depend on the level of behavior.
1. Skill-based behavior
2. Rule-based behavior
3. Knowledge-based behavior
Error Reduction
Selection of personnel with skills and
capabilities (perceptual, intellectual, motor
skills, etc.)
1. Not easy to determine skills required.
2. Few reliable tests for measuring skill levels.
3. Limited supply of qualified people.
Error Reduction
Proper training of personnel reduces errors.
Old habits are hard to break.
Training can be expensive.
Error Reduction
Particular errors made impossible to commit
Particular errors made difficult to commit
Consequences of errors reduced in severity
Human Biases
People give an undue amount of weight to early
evidence or information.
Humans are generally conservative and do not
extract as much information from sources as
they optimally should.
The subjective odds in favor of one alternative or
the other are not assessed to be as extreme or
given as much confidence as optimally they
Human Biases - continued
As more information is gathered, people become
more confident in their decisions,
but not necessarily more accurate.
Humans have a tendency to seek far more
information than they can absorb adequately.
People often treat all information as if it were
equally reliable.
Human Biases - continued
People cannot entertain more than a few
(three or four) hypotheses at a time.
People tend to focus on only a few critical
attributes at a time and consider only about
two to four possible choices that are ranked
highest of those few critical attributes.
People tend to seek information that confirms
the chosen course of action and to avoid
information or tests whose outcome could
disconfirm the choice. (Confirmation Bias)
Human Biases - continued
A potential loss is viewed as having greater
than a gain of the same amount. (Risk Aversion)
People believe that mildly positive outcomes are
more likely than either mildly negative or highly
positive outcomes.
People tend to believe that highly negative
outcomes are less likely than mildly negative