HUMAN ERROR

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HUMAN ERROR

• Nantida Wisawayodhin M Sc. M.Erg.S.

Module Cognition and Information
Processing Course Human Centered Design
(HCD) SOAD, KMUTT
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OVERVIEW

• Introduction
• Human error
• Error types
• Cognitive stages and error type
• Level of performance and human error
• Failure mode
• Error forms and schemata
• GEMS
• Error detection and correction
• Active vs. Latent errors
• Practical based on an air crash documentary

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INTRODUCTION
What is human error? Have you made any errors
today?
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INTRODUCTION

• Whats wrong with this picture?

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INTRODUCTION

• To err is human

Alexander Pope An Essay on Criticism, 1711
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INTRODUCTION

• We make errors far less frequently than making
  correct actions, but when they occurs, the
  consequences can be disastrous.

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INTRODUCTION

• Chernobyl disaster in 1986
• The explosion of a reactor of a nuclear power
  station in former Russia releasing radioactive
  material into the atmosphere immediately costing
  over 30 lives (and countless thousands during
  clean-ups), contaminated over 400 square miles
  around the plant.
• Twenty years on it still has far reaching effects
  on the environment and health of the whole of
  Western Europe and the Scandinavia.

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INTRODUCTION

• The Herald of Free Enterprise in 1987
• A roll-on/roll-off passenger and freight ferry
  that left Zeebrugge, Belgium en route to Dover,
  England with her bow door open and capsized 20
  minutes later costing nearly 200 lives and
  numerous injures.

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INTRODUCTION

• Bhopal in 1984
• A leakage of around 43,000 kilograms of an
  extremely toxic chemical, methyl isocyanate, from
  a small pesticide plant in the central India city
  of Bhopal that killed at least 2,500 people and
  injured more than 200,000.

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INTRODUCTION

• Can we be error-free?
• The simple answer is no
• As long as human is still the decision maker and
  the problem solver, it is not possible to totally
  eradicate errors

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INTRODUCTION

• But we can try to reduce the occurrence of human
  error by trying to understand what human error
  is, the types of error, how it occurs and why it
  occurs.

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HUMAN ERROR

• Influencing factors in error production

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HUMAN ERROR

• What is human error?
• An error is a departure from the intended path
  and the desired goal
• In order to get to a desired goal, one must have
  an intention
• To have an intention, one must be aware of the
  situation and pay attention to it
• Human error, intention and attention are in
  separable
• An action without intention cannot produce a
  human error

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INTENTION AND HUMAN ERROR

• What is an intention?
• An expression of the end-state (goal) to be
  attained
• An indication of the means (plan) by which it is
  to be achieved
• Components of an intention
• A desired goal
• Sub-goals
• A formulation of a plan
• Action execution

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INTENTION AND HUMAN ERROR

• Example making a cup of coffee
• A desired goal a cup of coffee
• Sub-goals 1) boil water 2) put coffee in cup
  3) pour boiled water in cup 4) add milk and
  sugar and 5) stir
• A formulation of a plan retaining memory on how
  to achieve the sub-goals
• Action execution physically make a cup of coffee

Error could occur anywhere along this path
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INTENTION, ATTENTION AND ERROR
Mistakes
(Absent mindedness)
Slips Lapses
Intended path
Deviation from intended path
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INTENTION AND HUMAN ERROR

• Examples of error
• Forming sub-goals
• Have an incorrect understanding (incorrect
  knowledge) of the situation and therefore, set an
  incorrect sub-goal
• Formulating a plan
• Having set an appropriate goal, one could apply a
  wrong rule (procedural knowledge IF(situation),
  THEN(situation/action) rules) in order to achieve
  the goal.
• Action execution
• Error at this level is when one forgets what
  he/she is intended to do (memory failure) or
  executes the wrong action due to attentional
  failure.

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HUMAN ERROR

• Therefore human error is
• All occasions in which a planned sequence of
  mental or physical activities fails to achieve
  its intended outcome, and when these failures
  cannot be attributed to the intervention of some
  chance agency.
• (Reason, 1990)

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HUMAN ERROR TYPES

• Slips errors result from some failure in the
  execution stage of an action sequence, regardless
  of whether or not the plan which guided them was
  adequate to achieve its objective
• accidentally pressed the Delete button when
  intended to press the Backspace button on the
  keyboard
• Lapses errors result from some failure in the
  storage stage of an action sequence, regardless
  of whether or not the plan which guided them was
  adequate to achieve its objective
• want some orange juice, walk to the fridge, open
  it and then forgot what you actually open the
  fridge for
• Mistakes deficiencies or failures in the
  judgemental and/or inferential processes involved
  in the selection of an objective or in the
  specification of the means to achieve it,
  irrespective of whether or not the actions
  directed by this decision-scheme run according to
  plan
• Bhopal - repressurising the pesticide tank having
  failed to achieve it on the previous attempt
  resulting in leakage of toxic chemical into the
  atmosphere without checking for cause of failure

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HUMAN ERROR TYPES
Norman summarized the distinction between
mistakes and slips/lapses as If the intention
is not appropriate, this is a mistake. If the
action is not what was intended, this is a
slip. (Norman, 1983)
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COGNITIVE STAGES AND ERROR TYPES
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COGNITIVE STAGES AND ERROR TYPE
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THREE LEVELS OF PERFORMANCE

• Rasmussen (1984) SRB model
• Describes human performance as having three
  levels of complexity
• The application of each level is determined by
  the levels of familiarity with the environment or
  task
• Basic level of complexity skill-based
  performance
• Medium level of complexity rule-based
  performance
• High level of complexity knowledge-based
  performance

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THREE LEVELS OF PERFORMANCE

• SRK model
• Skill-based (SB) performance
• Sensorimotor performance take place without
  conscious control as smooth, automated, and
  highly integrated patterns of behaviour
• Based on patterns stored in long-term memory
• Example cycling, musical performance,
  touch-typing

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THREE LEVELS OF PERFORMANCE

• SRK model
• Rule-based (RB) performance
• Consists of a goal-oriented sequence of
  subroutines in a familiar work situation (rules)
• Subroutines based on stored rules formed from
  previous experiences
• Very often, the goal is not explicitly
  formulated, but is found implicitly in the
  situation releasing the stored rules
• Example car driving, aircraft control,
  mathematical problem solving

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THREE LEVELS OF PERFORMANCE

• SRK model
• Knowledge-based (KB) performance
• Relies upon a feedback control and a "mental
  model" of the system in question
• Used only when the stock of stored
  problem-solving routines is exhausted
• Slow, sequential, laborious and resource-limited
  conscious processing
• Process setting local goals, initiating actions
  to achieve them, observing the extent to which
  the actions are successful and then modifying
  them to minimize the discrepancy between the
  presented position and the desired state.

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LEVEL OF PERFORMANCE AND ERROR TYPE
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MEMORY AND ERROR TYPES
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KNOWLEDGE-BASED MISTAKES

• Occur in decision making stage
• Incorrect plans of action are arrived at because
  of a failure to understand the situation
  (incorrect knowledge)
• Make use of declarative knowledge
• Put heavy demands on attentional resources and
  the central executive
• Often involves in fault diagnosis,
  troubleshooting and reasoning in a novel
  situation
• Example medical diagnosis of a rare disease,
  reading of new cosmos pictures

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RULE-BASED MISTAKES

• Occur in the decision making stage
• Occur when the situation is familiar because they
  have encountered similar situations in the past
• Make use of existing (IF(situation),
  THEN(situation/action)) rules in the procedural
  knowledge
• Example IF the patient has fever, runny nose
  and sneeze a lot, THEN the patient has influenza
• Mistakes occur when the IF part of the rule
  invoked do not match the actual situation
• Example Braking hard is an appropriate rule on a
  normal road, but would be dangerous on a slippery
  or icy road

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SKILL-BASED LAPSES

• Occur as a result of memory failure at the
  execution stage
• What we often called forgetfulness
• Omission of action from a familiar sequence of
  actions
• Often due to interruption of thought resulting in
  momentary attentional failure
• Occur frequently in maintenance and installation
  procedures
• Example Forgetting to remove the last page from
  the photocopier machine Forget to tighten a
  screw during a maintenance session

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SKIL-BASED SLIPS

• Occur in the response execution stage
• The right intention and plan is formed, but
  incorrectly carried out
• Sometimes termed a commission error
• Involve in a routine and fairly automatic task in
  a familiar setting
• Require minimum attentional resource and central
  executive
• Can be due to either inattention or overattention

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MODEL OF UNSAFE ACT
A deliberate action to break social rules. Not
included in our discussion
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EXERCISE

• 2 groups of 3
• Identify the error type of each of the error
  presented on the piece of paper
• Provide the reason why you choose that error type
• 10 minutes

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BREAK

• 15 MINUTES

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FAILURE MODE AT EACH LEVEL OF PERFORMANCE
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FAILURE MODE AT SB LEVEL

• Inattention
• Capture errors
• attention momentarily redirected to internal
  preoccupation or external distractor at a time
  that it is needed to set the action along the
  currently intended pathway
• Activation of incorrect but stronger schema due
  to shared attributes
• the current action departs from the norm
• Interruption by the occurrence of external events
• Answer the phone in the middle of thinking
  forgot the train of thought

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FAILURE MODE AT SB LEVEL

• Inattention continue
• Time delay between the formulation of intention
  and the action
• Perceptual confusion mistaking a similar object
  to be the target object
• Entangling of two active schemata
• Overattention
• When attention is paid to the task at hand at an
  inappropriate time resulting in the disruption to
  the smooth running of an automated task
• Example Become aware of hand movements during
  touch typing

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FAILURE MODE AT RB LEVEL

• Strong-but-wrong rule from first impression
• Explain away of countersigns (information against
  the activation of a particular rule) and
  mistaking non-signs (irrelevant information to
  the decision) as signs (information that satisfy
  the activation of that rules)
• Information overload
• Rule strength strong (often used and successful)
  rules need less increase in activation level to
  be activated

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FAILURE MODE AT KB LEVEL

• Insufficient knowledge or expertise (incorrect
  mental models)
• Working memory overload
• Out of sight out of mind
• Confirmation bias
• Fail to consider all the alternatives
• Biased reviewing
• Overconfidence
• Experts tend to be confident in the correctness
  of their knowledge

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ERROR FORM AND SCHEMA

• Varied forms due the nature of how we store our
  knowledge in the long-term memory and the
  external situations the errors occur in
• How schemata are activated also plays a role in
  the varied and unpredictable nature of the forms
  of error

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SCHEMA ACTIVATION SIMILARITY MATCHING

• The matching of the attributes within the
  schemata and the relevant information in the
  external world and the current intention.
• Types of information used to create the matching
  are called specific activators because they
  activate specific schemata which contain them.
• The schema which is activated and brought into
  consciousness tends to be appropriate to the
  situation.

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SCHEMA ACTIVATION FREQUENCY GAMBLING

• When there are inadequate numbers of specific
  activators in the external environment leading to
  the increase in activation level of many
  schemata.
• In this situation the general activators are
  relied on heavily to select a schema for the
  situation.
• The general activators include recency and
  frequency of activation

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OBSEVABLE ERRORS
List of observable error behaviour
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Reasons GEMS model
Transition from one level of performance to the
next and the error mechanisms operating at all
three levels of performance
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Switching between levels

• SB RB level
• Attentional checks result in a detection of a
  deviation from the planned-for condition
• Attempt to apply a rule to correct the situation.
  
• If the corrective rules are easily found and
  successfully applied, performance is returned to
  the SB level
• RB KB level
• When the problem solver realise that none of the
  RB solutions available is adequate to solve the
  problem
• Repeated cycles between KB and RB levels as
  various possibilities are explored
• KB SB level
• When an adequate solution is found.
• A formulation of a new plan of action requiring
  the execution of a fresh set of SB routine

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ERROR DETECTION AND CORRECTION RATE

• Performance at each level
• SB and RB performance happen far more frequently
  than KB performance
• But opportunity for errors in the KB level of
  performance is a lot higher
• Proportion of errors out of all errors studied
  (based on three studies)
• SB errors 60.7
• RB errors 27.1
• KB errors 11.3
• Detection rate
• SB 86.1
• RB 73.2
• KB 70.5
• Correction rate
• SB twice as high as those for RB errors (almost
  all detected are corrected)
• RB three times as high as those for KB errors
• KB poor record of error correction

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LATENT vs. ACTIVE FAILURS

• Active failures
• Associated with the direct interaction between
  the user and the product or system
• Effects are felt almost immediately
• So far we have been considering the different
  types and forms of active failures
• Latent failures
• Adverse consequences that lie formant within the
  system for a long time, only becoming evident in
  combination with other factors
• Activities removed in time and space from the
  direct control interface
• Incorrect installation, faulty maintenance, bad
  management decision
• Designers role in system failure
• Often designers contribution to accidents or
  incidents are as latent failures as a result of
  poor design

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Swiss cheese model illustrating the complex
interaction between latent and active failures
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REFERENCES

• Norman, D.A. 1988. The Design of Everyday
  Things. New York Basic Books
• Reason, J. 1990. Human Error. Cambridge
  University Press.
• Wickens and Holland. 2000. Engineering Psychology
  and Human Performance. Chapter 12

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Any Questions?
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CASE STUDY

• National Geographic Air Crash Investigation
  Seconds from Disaster
• A reconstruction of an air crash over Kegworth
  meters away from the M1 motorway and 900 meters
  short of the runway in June 1989 by the National
  Geographic. The airplane broke into 3 pieces from
  the crash with 47 losses of lives.
• This is a example of the contribution of latent
  failure over active failure and the effect of
  interface design on human error.
• This video also gives a good introduction to the
  next class on mental workload and situation
  awareness.

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PRACTICAL

• An essay answering the following questions
• What are the latent and active failures that
  contribute to the accident?
• Specify design related issues as illustrated by
  the VDO clip and how these changes in the design
  affect the pilots performance.
• What do you think could be learnt from this
  accident that could prevent a similar accident
  from occurring (give suggestions on what could be
  done at mechanical design stage, interface design
  stage and training stage and how the suggestions
  might improve the situation)?