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.


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.


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)


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.


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.


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.


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.


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.


Halo effects – Difficulty if processing independently two separate orderings of the same people or objects.


Problems with causality – Over simplification. Underestimating future irregularities

because of past experience . Creeping determinism. The illusion of control.


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


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.


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.


QUESTION????

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Human Error