Dick de Waard - Human Error Classification
Reason - Chapter 2
The Nature of Error
● Error is tied to human intention and arises when planned actions fail to achieve their
intended outcomes, barring external chance factors.
● Not all errors are negative; some can lead to learning, innovation, or unexpected
benefits, such as trial-and-error discoveries.
Plans as the Foundation of Actions
● Human behavior is structured around plans, which range from short-term, specific
objectives (e.g., choosing a meal) to long-term goals (e.g., dieting).
● Conflicts between overlapping plans often reveal the complexity of human
decision-making and the potential for error. For example, a successful short-term plan to
eat a rich meal may undermine the broader goal of weight loss.
Failures
● Execution Failures (Slips and Lapses): Occur when actions deviate from the intended
plan, often due to distraction, absent-mindedness, or clumsiness.
● Planning Failures (Mistakes): Arise when actions align with a plan that is inherently
flawed, often involving poor judgment or inadequate reasoning.
,Consequences
● The impact of an error depends on context.
- Minor errors, like pressing the wrong button at home, might be trivial
- similar errors in critical environments, such as a nuclear power plant, can be
disastrous.
→ Errors reflect the interplay between human limitations, environmental conditions, and the
broader systems within which actions take place.
Human Capacity and Constraints:
● Human performance is limited by physical and mental capacities
- Although we juggle multiple plans, only one tends to dominate at a given moment.
● This limitation is a double-edged sword, helping to prioritize focus but also creating
vulnerability to errors when plans conflict or exceed capacity.
Defining Error
● Reason offers a working definition: error encompasses occasions where planned actions
fail to achieve desired goals without chance interventions.
→ He distinguishes between avoidable errors tied to intention and unavoidable consequences
of random external events.
! Errors are not simply individual failings but are shaped by systemic, environmental, and
situational factors.
! Understanding error requires a nuanced approach, examining not just immediate actions but
also the broader context of planning, intention, and execution.
Reason - Chapter 3
James Reason introduces a framework for categorizing human error through three performance
levels: skill-based (SB), rule-based (RB), and knowledge-based (KB), a model developed by
Jens Rasmussen.
→ SB Level: Routine, automatic actions with minimal conscious control, disrupted by
interruptions or attentional shifts.
→ RB Level: Predefined rules govern actions. These are activated when problems are
recognized, but their reliability depends on accurate situational diagnosis.
, → KB Level: Relies on feedback and conscious reasoning for novel problems. This level
demands active engagement, making it resource-intensive and prone to error due to incomplete
or inaccurate internal models.
Control Modes
Feed-Forward Control (SB and RB Levels): Actions are guided by stored schemas or
rules, enabling efficient responses in familiar situations.
Feedback Control (KB Level): Requires ongoing adjustment and assessment of
outcomes, often involving trial and error, which increases the likelihood of mistakes.
The Nature of Errors Across Levels
● Slips and Lapses: Occur at the SB level, involving unintended actions during routine,
automatic tasks. These errors arise from procedural habits and schemas being
unintentionally activated.
● Rule-Based Mistakes: Occur at the RB level, when individuals apply incorrect
diagnostic or procedural rules to familiar problems. These errors stem from strong but
contextually inappropriate reliance on established rules.
● Knowledge-Based Mistakes: Occur at the KB level, where individuals face novel
problems requiring active problem-solving and decision-making. Errors here are tied to
limitations in reasoning, incomplete knowledge, and the labor-intensive nature of
trial-and-error processes.
Expertise and Error Predictability
● Expertise primarily resides at the RB level
→ where experienced individuals rely on a vast repertoire of abstract and robust rules.
However, highly skilled individuals are prone to "strong-but-wrong" errors when
automatic actions or rules are misapplied.
● Novices and experts face different challenges
→ novices struggle with KB-level tasks due to limited knowledge, while experts are more
vulnerable to execution-level slips and rule-based mistakes.
→ Human activities often involve all three performance levels simultaneously. For example,
driving combines automatic SB-level actions (steering), RB-level rule application (traffic laws),
and occasional KB-level problem-solving (navigating detours).
Reason - Chapter 2
The Nature of Error
● Error is tied to human intention and arises when planned actions fail to achieve their
intended outcomes, barring external chance factors.
● Not all errors are negative; some can lead to learning, innovation, or unexpected
benefits, such as trial-and-error discoveries.
Plans as the Foundation of Actions
● Human behavior is structured around plans, which range from short-term, specific
objectives (e.g., choosing a meal) to long-term goals (e.g., dieting).
● Conflicts between overlapping plans often reveal the complexity of human
decision-making and the potential for error. For example, a successful short-term plan to
eat a rich meal may undermine the broader goal of weight loss.
Failures
● Execution Failures (Slips and Lapses): Occur when actions deviate from the intended
plan, often due to distraction, absent-mindedness, or clumsiness.
● Planning Failures (Mistakes): Arise when actions align with a plan that is inherently
flawed, often involving poor judgment or inadequate reasoning.
,Consequences
● The impact of an error depends on context.
- Minor errors, like pressing the wrong button at home, might be trivial
- similar errors in critical environments, such as a nuclear power plant, can be
disastrous.
→ Errors reflect the interplay between human limitations, environmental conditions, and the
broader systems within which actions take place.
Human Capacity and Constraints:
● Human performance is limited by physical and mental capacities
- Although we juggle multiple plans, only one tends to dominate at a given moment.
● This limitation is a double-edged sword, helping to prioritize focus but also creating
vulnerability to errors when plans conflict or exceed capacity.
Defining Error
● Reason offers a working definition: error encompasses occasions where planned actions
fail to achieve desired goals without chance interventions.
→ He distinguishes between avoidable errors tied to intention and unavoidable consequences
of random external events.
! Errors are not simply individual failings but are shaped by systemic, environmental, and
situational factors.
! Understanding error requires a nuanced approach, examining not just immediate actions but
also the broader context of planning, intention, and execution.
Reason - Chapter 3
James Reason introduces a framework for categorizing human error through three performance
levels: skill-based (SB), rule-based (RB), and knowledge-based (KB), a model developed by
Jens Rasmussen.
→ SB Level: Routine, automatic actions with minimal conscious control, disrupted by
interruptions or attentional shifts.
→ RB Level: Predefined rules govern actions. These are activated when problems are
recognized, but their reliability depends on accurate situational diagnosis.
, → KB Level: Relies on feedback and conscious reasoning for novel problems. This level
demands active engagement, making it resource-intensive and prone to error due to incomplete
or inaccurate internal models.
Control Modes
Feed-Forward Control (SB and RB Levels): Actions are guided by stored schemas or
rules, enabling efficient responses in familiar situations.
Feedback Control (KB Level): Requires ongoing adjustment and assessment of
outcomes, often involving trial and error, which increases the likelihood of mistakes.
The Nature of Errors Across Levels
● Slips and Lapses: Occur at the SB level, involving unintended actions during routine,
automatic tasks. These errors arise from procedural habits and schemas being
unintentionally activated.
● Rule-Based Mistakes: Occur at the RB level, when individuals apply incorrect
diagnostic or procedural rules to familiar problems. These errors stem from strong but
contextually inappropriate reliance on established rules.
● Knowledge-Based Mistakes: Occur at the KB level, where individuals face novel
problems requiring active problem-solving and decision-making. Errors here are tied to
limitations in reasoning, incomplete knowledge, and the labor-intensive nature of
trial-and-error processes.
Expertise and Error Predictability
● Expertise primarily resides at the RB level
→ where experienced individuals rely on a vast repertoire of abstract and robust rules.
However, highly skilled individuals are prone to "strong-but-wrong" errors when
automatic actions or rules are misapplied.
● Novices and experts face different challenges
→ novices struggle with KB-level tasks due to limited knowledge, while experts are more
vulnerable to execution-level slips and rule-based mistakes.
→ Human activities often involve all three performance levels simultaneously. For example,
driving combines automatic SB-level actions (steering), RB-level rule application (traffic laws),
and occasional KB-level problem-solving (navigating detours).
