Human Error
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Transcript of Human Error
Mashrura MusharrafHKR 6350
HUMAN ERROR
CHAPTER 3:PERFORMANCE
LEVELS & ERROR TYPES
Why the slips – mistakes dichotomy is not enough?
Distinguishing three error types
A generic error- modelling system (GEMS)
Failure modes at the skill based levels
Failure modes at the rule based levels
Failure modes at the knowledge based levels
OUTLINE
Oyster Creek (1979): Operator intended to close valves A and E, inadvertently closed B and C also.
Ginna (1982) The operators, intending to depressurize the reactor cooling system, used the wrong strategy with regard to the pressure relief valve.
Easy to be categorized in either Slip or Mistake.
WHY SLIP MISTAKE DICHOTOMY NOT ENOUGH
Oyster Creek (1979) Operators mistook the annulus level for the water level within the shroud. The low water level alarm ignored.
Three Mile Island (1979) No recognition of the relief valve open. Failure of panel display not taken into account.
SLIP/MISTAKE???????????????? Improper appraisal on system state – Mistake ‘Strong but wrong’ interpretation selected – Slip
WHY SLIP MISTAKE DICHOTOMY NOT ENOUGH
Solution – Two kinds of mistake – Rule based mistakes and Knowledge based mistakes
Finally, three distinct error types
ERROR TYPES
Performance level Error TypeSkill-based level Slips and lapsesRule-based level RB MistakesKnowledge-based level KB Mistakes
Is an individual engaged in problem solving at the time an error occurred???
SB level – Precede problem detection Routine works
RB and KB level – Occurs during subsequent attempts to find a solution Involves problem solving
DISTINGUISHING THREE ERROR TYPES
TYPE OF ACTIVITY
Slip – Distraction/Preoccupation leads the focus elsewhere than the routine task.
RB/KB Mistake – Focus do not stray far from some feature of problem configuration.
FOCUS OF ATTENTION
SB Slips and RB Mistakes – SB level –
Performance based on feed forward control. Depends upon a very flexible and efficient dynamic internal
world model.
RB level – Performance goal oriented, structured by feed forward control
through stored rule. Rule/Control selected from previous successful experiences.
KB Level – Feedback control. Store exhausted, work online, actions taken and then
modified to minimize discrepancy. -> Error Driven.
CONTROL MODE
SB and RB level – Easier to predict, error forms available within individuals inventory of knowledge structure.
SB level – Attentional check is omitted or mistimed.
RB level – inappropriate matching of environmental signs to the situational component of well tried rules.
KB level – large problem space, less easy to specify the short-cuts that may encounter error.
EXPERTISE AND PREDICTABILITY
SB level – Experts and novices have differences in the level and complexity of knowledge representation.
RB level – Experts have much larger collection of problem solving rules than novices.
KB level – Less likely to be related with expertise. Even expert can perform worse than novice in an unfamiliar situation.
EXPERTISE AND PREDICTABILITY
SB error and RB error greatly exceed those specifically due to KB failures.
However, if expressed as proportions of the total number of opportunities for error, percentage of errors in the SB and RB modes very smaller than KB level.
RATIO OF ERROR TO OPPORTUNITY
SB level – Attentional Capture and Strength (relative frequency of successful execution).
RB level – Detailed knowledge of the task, Operator’s training.
KB level – Mistakes can take wide variety of forms, not dependent on past experience or knowledge stock.
Mistakes are harder to detect than slips.
INFLUENCE OF SITUATIONAL FACTORS & DETECTABILITY
SB level – Nature and time of change potentially knowable and actor possesses routine to deal with. Concern – Timely investment of an attentional check.
RB level – Changes anticipated but the time of occurrence is not known in advance. Concern – Mistake may arise by adopting a bad rule or
misapplication of a good rule.
KB level – Change fall outside the scope of prior experience or forethought and has to be dealt with by error prone ‘on-line’ reasoning.
RELATIONSHIP TO CHANGE
DISTINGUISHING ERROR TYPES
Operations divided into two areas – Those that precede the detection of a problem Those that follow it
Monitoring failures – Involves checking Whether actions are running according to plan Whether the plan is still adequate
Problem solving failures –“Humans, if given a choice, would prefer to act as context-specific pattern recognizers rather than attempting calculate or optimize.”
A GENERIC ERROR MODELLING SYSTEM (GEMS)
GEMS
GEMS
Inattention Over attentionDouble-capture slips
Omissions following interruptions
Reduced intentionality
Perceptual confusions
Interference errors
Omissions
Repetitions
Reversals
FAILURE MODES OF SKILL BASED LEVEL
Double-capture slips - The mechanism where attention is captured by some distraction and some triggering cue is missed, and the activity is captured by the most active schema (usually the most commonly used alternative leading away from the point where the cue was overlooked)
Old habit intrusionStrong habit exclusionBranching errorOvershooting a stop ruleFailure to attend need for change
INATTENTION
Omissions associated with interruptions – Failure to make an attentional check is compounded by some external event.
“I picked up my coat to go out when the phone rang. I answered it and then went out of the front door without my coat.”
Reduced intentionality – Delay intervenes between the formulation of intention and execution. Failure to make periodically refreshed attentional checks result in slip.
Detached intentions Environmental capture Multiple sidesteps
INATTENTION
Sometimes reduced intentionality takes the form of state rather than actions. What am I doing here! I should be doing something but I cant remember what!
Perceptual confusions – Recognition schemata accept as a match for the proper object something that looks like it, is in the expected location or does a similar job.
Accepting look-alikes for the intended object Pouring/placing something into a similar but unintended
receptacle.
INATTENTION
Inference errors: blends and spoonerisms – Two currently active plans or, within a single plan, two action elements, can become entangled in the struggle to gain control of the effectors. Results in –
Inappropriate blends of speech and action .
Transposition of actions within the same sequence producing a behavioral spoonerism.
INATTENTION
Focal attention interrogates the progress of an action sequence at a time when control is best left to the automatic ‘pilot’. Omission – One concludes that the process is further along
than it actually is, and, as a consequence, omits some necessary step.
Repetition – One decides that it has not yet reached the point where it actually is and then repeats an action already done.
Reversal – An inappropriately timed check can cause an action sequence to double back on itself.
OVER ATTENTION: MISTIMED CHECKS
The framework is proposed by Holland, Holyoak, Nisbett and Thagard (1986).
A number of rules compete for the right to represent the current state.
Prerequisite – Matching the condition part of the rule with state features.
Strength – The number of times a rule has performed successfully.
Support – Degree of compatibility it has with currently active information.
CONCEPTUAL FRAMEWORK TO IDENTIFY FAILURE MODES AT RB LEVEL
HIERARCHICAL MODEL
Most General/ Prototypical rule
Most Exceptional rule
Additional ExceptionDefault
expectation
Misapplication of good rule Application of bad rulesFirst exceptions
Countersigns and nonsigns
Informational overload
Rule strength
General rules
Redundancy
Rigidity
Encoding deficiencies
Action deficiencies•Wrong rules•Inelegant rules•Inadvisable rules
FAILURE MODES AT THE RULE BASED LEVEL
The first exceptions – On the first occasion an individual encounters a significant exception to a general rule, particularly if that rule has repeatedly shown itself to be reliable in the past, the strong but now wrong rule will be applied. Oyster Creek (1979)
Signs, countersigns and nonsigns Signs – inputs that satisfy some or all of the conditional
aspects of appropriate rule. Countersigns – inputs that indicate that the more general
rule is inapplicable. Nonsigns – inputs which do not relate to any existing rule,
but which constitute noise within the pattern recognition system.
MISAPPLICATION OF GOOD RULE
Informational overload – Detection of countersigns become more difficult by the abundance of information. Local state indications>> Cognitive system’s ability to
apprehend them.
Rule strength – If possibility of partial matching is allowed, the cognitive system is biased to favor strong rather than weak rules whenever the matching conditions are less than perfect.
Partial matching is the one preferred here, since it allows for a trade off between the degree of matching and the strength of the rule.
MISAPPLICATION OF GOOD RULE
General rules are likely to be stronger – Relationship between level and rule strength is positive.
General rule -> Greater frequency of encounter the world -> stronger
Exceptional rule -> Exceptional by definition
Redundancy – Repeated encounters with a given problem configuration allow to identify certain features to be more significant than others. Results in bias to favor previously informative signs rather than the rarer countersigns.
MISAPPLICATION OF GOOD RULE
Rigidity – Stubborn tendency towards applying the familiar but cumbersome solution, when simpler, more elegant solutions are readily available.
General versus specific rules – Real life situation – Strong but wrong rule (Higher level) Less complicated world (psychological laboratory) – More
specific rules (lower level)
MISAPPLICATION OF GOOD RULE
Two Broad categories –
Encoding deficiency – Features of a particular situation are either not encoded at all or are misrepresented.
Action deficiency – The action component yields unsuitable, inelegant or inadvisable responses.
THE APPLICATION OF BAD RULES
Three stage process oriented framework proposed by Karmiloff-Smith. Phase 1. Procedural Phase-
Output is primarily data-driven. Control resides mostly at the knowledge based level. Problem solving online results in a large unorganized mass of
routines. Phase 2. Metaprocedural Phase –
Earlier procedural representations is the problem space. Procedural rules are organized into meaningful categories.
Control resides on ‘top-down’ knowledge structure. Results in overenthusiastic application of global rules, missing
exceptions. Phase 3. Conceptual Phase -
Control resides on the interaction between data-driven and top-down processing.
A DEVELOPMENTAL PERSPECTIVE
Certain properties of the problem space are not encoded at all. Balance Beam Problem –
Magnitude of the weight Distance from fulcrum
ENCODING DEFICIENCIES
Certain properties of the problem space may be encoded inaccurately. Trajectory of a ball emerging from a coiled tube.
ENCODING DEFICIENCIES
An erroneous general rule may be protected by the existence of domain specific exception rules.
Of course impetus theory is good for predicting the motion of object is conditions of constant friction.
ENCODING DEFICIENCIES
Wrong rules . Subtraction problem – When borrowing is actually needed?
Inelegant or clumsy rules Problems may have multiple routes to solution. Inelegant routes may become established as part of rule
based storage.
Inadvisable rules Solution mostly adequate to achieve its immediate goal. BUT regular employment lead, on occasions, to avoidable
accidents.
ACTION DEFICIENCY
Failures that arise when the problem solver has to resort to computationally powerful yet slow, serial and effortful ‘on-line’ reasoning originated from two basic sources: ‘bounded rationality’ and an incomplete mental model of the problem space.
FAILURE MODES AT KNOWLEDGE BASE LEVEL
THREE TYPES OF PROBLEM CONFIGURATION
2 types of Multiple Dynamic problem –•Bounded•Complex
Knowledge-based performanceSelectivityWorkspace limitationsOut of sight out of mindConfirmation bias OverconfidenceBiased reviewingIllusory correlationHalo effectsProblems with complexity•Problems with delayed feed-back•Insufficient consideration of processes in time•Difficulties with exponential developments•Thinking in causal series not causal nets•Thematic vagabonding•Encysting
FACTORS FOR FAILURE AT KB LEVEL
Selectivity – Attention is given to the wrong features Attention not given to the right features
Workspace limitation – Features are interpreted by fitting them into an integrated
mental model. Validity of inference lies on searching different models of
the situation. Becomes heavy burden upon finite resources.
Out of sight out of mind – Availability heuristic – Undue weight to facts that readily come in mind. Ignore which is not immediately present.
FACTORS FOR FAILURE AT KB LEVEL
Confirmation bias – In the face of ambiguity, rapidly favors one available
interpretation and is then unwilling to part with it.
Overconfidence – Justify action by focusing on positive evidence and
neglecting contradictory evidence. Further accompanied by confirmation bias originated from a
completed plan of action.
FACTORS FOR FAILURE AT KB LEVEL
Why plans left unmodified? Plan is very elaborate Plan is the product of considerable labor and investment Plan is the product of several people Plan has hidden objectives
Biased reviewing: the “check off” illusion – Have I taken account of all possible factors????
Illusory correlation Solvers often poor at detecting covariation. Partly they have little understanding, and partly they are
disposed to detect covariation only when their theories are likely to predict it.
FACTORS FOR FAILURE AT KB LEVEL
Halo effects – Difficulty if processing independently two separate orderings of the same people or objects.
FACTORS FOR FAILURE AT KB LEVEL
Problems with causality – Over simplification. Underestimating future irregularities
because of past experience . Creeping determinism. The illusion of control.
FACTORS FOR FAILURE AT KB LEVEL
Problems with complexity – Problems with delayed feed-back – Subjects lose synchrony
with the current situation and always lag behind actual events.
Primary mistake (All subject) Insufficient consideration of processes in time – Interest lies
on how things are now, neglecting how they had developed.
Difficulties in dealing with exponential development – What does 6% annual growth in registered cars means???
Thinking in causal series instead of causal nets
FACTORS FOR FAILURE AT KB LEVEL
Mistakes of subject with poor performance –
Thematic vagabonding – Switching from issue to issue quickly, treating each one superficially. Denoted as Escape behavior.
Encysting – Non important issues are attended to small details, while other important issues are disregarded.
FACTORS FOR FAILURE AT KB LEVEL
Problems of diagnosis in everyday situations
Root cause is the complex interaction between two logical reasoning tasks.
To identify critical symptoms and factual elements needing an explanation.
Verifying whether symptoms have been explained and supplied factors are compatible with scenario.
FACTORS FOR FAILURE AT KB LEVEL
QUESTION????