The Butterfly Ballot CMPE 233: Human Factors
Human Errors
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Why did this error happen? How common? ►Ballot violates conceptual model ►Ballot violates S-R compatibility (natural mappings): ► Human operator accounted for over 90 % of the documented no collocation or congruence between stimulus and air traffic control system errors response ► Over 50 % of all technical medical equipment problems are due to operator errors Arrangement of holes (response) incongruent with arrangement of names (stimulus) ► Up to 90 % of accidents both generally and in medical devices are caused by human mistakes Visual momentum from reading left-to-right suggests response to the right of the name ► A study of 23000 defects in the production of nuclear components revealed that approximately 82 % of the defects Violation to Gestalt principles of proximity: separating bar were due to human errors lead democratic vote to second punch hole ► During the period from June 1 1973 to June 30 1975, 401 ►Ability to detect and correct errors limited human errors occurred in US commercial light water nuclear No feedback to check response reactors No easy way to correct errors
James Reason’s Swiss Cheese model of What is human error? organizational accidents ►Sanders & McCormick (1976) Inappropriate or undesirable human decision or behavior that reduces, or has the potential for reducing, effectiveness, safety, or system performance Some holes due ►Reason (1990, 1997) to active failures Hazards 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 Local trigger or active failure: final event (in a series of events) that leads to a disaster Other holes due to Resident pathogens or latent conditions: collection of Losses latent conditions factors that represent an accident waiting to happen (because resources are diverted to more immediate Successive layers of defences needs) Taxonomy of Human Error Error classification ►What type of error did people commit with the ►Errors of commission butterfly ballot? ►Errors of omission Rasmussen’s SRK model
Mistakes Slips ►Intended errors Intended Unintended Knowledge Rule ►Unintended errors ►Violation Interpretation Plan Stimulus Violation Slip Lapse Action Mistake Evidence Situation Intention Execution Assessment of Action Failure of memory Knowledge- Rule-based mistake based mistake Forget step Lose place Lapses and Failure of attention Forget intention mode errors Intrusion Wrong procedure Memory Omission Reversal Misorder / Mistime step
SB, RB and KB errors Omits entite task ERRORS OF Dimension SB errors RB errors KB errors OMISSION type of activity routine actions problem-solving activities Omits a step in a task on something other than focus of attention directed at problem-related issues Selects wrong control the task in hand mainly by automatic processors limited, conscious Selection error control mode Misposition of controls (schemata) (stored rules) processes predictability of error largely predictable variable Issue wrong command on types (actions) (rules) info though absolute numbers may be high, these ratio of error to absolute numbers small, Errors of Sequence constitute a small proportion of the total number of opportunity to error but opportunity ratio high opportunities for error ERRORS OF influence of situational low to moderate; instrinsic factors (frequency of extrinsic factors likely to COMMISSION Too Early factors prior use) likely to exert the dominant influence dominate detection usually fairly difficult, and often only achieved through external Timing Errors ease of detection Too Late rapid and effective intervention when and how knowledge of change not changes not prepared for relationship to change anticipated change will Too Little accessed at proper time or anticipated Qualitative Errors occur unknown Too Much
(Reason, 1990, Human Error)
SB failure modes RB failure modes ►RB = tackling unfamiliar anticipated problems by ►SB = effortless routine actions that take place as stored rules which are learned by explicit training smooth, automated and highly integrated patterns of and by experience behavior ►Misapplication of good rules: ►Inattention (omitted checks): First exceptions (first-but-now-wrong rule) Omissions following interruptions Signs, countersigns and non-signs Delay between intention and execution Information overload Perceptual confusions Rule strength General rules Interference errors Redundancy ►Over-attention (mistimed checks): Rigidity Omissions ►Application of bad rules: Repetitions Encoding deficiencies in rules Reversals Action deficiencies in rules KB failure modes KB failure modes ►Selective processing of ►Problems with complexity: ►KB = tackling unfamiliar unanticipated problems information Problems with delayed through reasoning to diagnose and solve problems, Limitation of space in feedback identify deep features about a situation, adapt plans ► working memory Insufficient consideration of and responses to the needs of the situation in the processes in time (out ►Availability heuristic Difficulties with exponential absence of pre-packaged solutions of sight out of mind) developments ►Confirmation bias Thematic vagabonding ►Overconfidence (flitting from one topic or area of a problem to ►Biased reviewing another without sufficient ►Halo effect (expecting time or effort being based on previous response) expended to resolve the ►Hindsight bias (I knew it problem) all along) Encysting (paralysis by analysis)
Study of aircraft maintenance SRK performance ►Hobbs & Williamson, 2002, Ergonomics ►Observations of the work of 25 aircraft mechanics: Activity sampling technique Task analysis checklist 666 observations ►Interviews with 72 maintenance workers: Using critical incident technique 101 critical incidents reported 3 categories of incidents: ►Behavioral events: error / acceptable behavior ►Environmental events ►Equipment-related events
Outcomes of 101 critical incidents Errors and opportunities for errors Human error occurrence types Causes for the occurrence ► Design errors: the result of inadequate design, eg the placement of controls and displays so far apart that an operator is unable to use them in an effective manner ► Poor motivation of involved personnel ► Operator errors: the result of operator mistakes and the ► Poor training or skill of concerned personnel conditions that lead to operator errors include lack of proper ► Poor equipment design procedures, complex taxonomy, poor training and operator carelessness ► Inadequate or poorly written equipment operating and ► Assembly errors: occur during product assembly due to maintenance procedures humans ► Poor job environment: poor lighting, uncomfortable ► Inspection errors: occur because of <100% accuracy of temperature, high noise level, crowded work space, ,etc inspectors ► Maintenance errors: occur in the field due to oversights by the ► Inadequate work tools maintenance personnel ► Complex tasks ► Installations errors: occur due to various reasons including ► Poor work layout using the wrong installation related blueprints or instructions ► Handling errors: occur because of inadequate storage or transportation facilities
Where errors happen in the process More Psychological Categories ► Decision error: occur when the wrong decision is made after ►Perception error: mis/not heard, mis/not seen considering the situation Internal Error Mode Internal Error Mechanism ► Action error: are the result of no action ,incorrect action ,or the Perception performance of correct action on the wrong object when required Mishear Expectation ► Transmission error: occur when information that must be Mishearing information. Perceptual errors driven by expectations. Mis-see Confusion passed or to others is not sent, sent incorrectly, or sent to the Misreading, misperceiving, or misidentifying visual Misidentifications and misperceptions due to wrong destination information. similar or confusable of appearance or spatial position. ► Checking error: occur when system require checks, the No detection (auditory) Discrimination failure incorrect checks are made ,checks are omitted ,or correct Failing to detect, or being late to recognise the Failing to see or hear something that is vague or checks are made on the wrong object significance of, information. of short duration. No detection (visual) Tunnel vision ► Diagnostic errors: are the result of misinterpreting the actual Failing to detect or identify visual information, or Fixating, tunnelling or ‘black-holing’ on situation when an abnormal event occurs detecting information too late to be effective. information, to the exclusion of other relevant information. ► Retrieval errors: occur when required info either from an Overload individual, an individual memory, or from any other ref A large amount of incoming information. Distraction / Preoccupation source is not received or the incorrect info is received Momentary distraction or longer-term preoccupation.
More Psychological Categories More Psychological Categories ►Memory error: forgotten, mis/not recalled ►Decision error: planning, decision making
Internal Error Mode Internal Error Mechanism Internal Error Mode Internal Error Mechanism Memory Decision Making
Omitted or late action Confusion Misprojection Misinterpretation Forgetting to perform a planned task, or missing a Other (e.g. similar) information interferes with Misprojecting or misjudging spatial-temporal Failure to integrate, calculate or understand step in a task sequence (including monitoring memory. information information. information/people). Poor decision or poor plan Failure to consider side- or long-term effects Forget information Overload Forgetting information or previous actions. Too much information to retain in memory. Poor decision or inadequate plan. Unforeseen side- or long-term effects. Misrecall information Insufficient learning Late decision or late plan Mind set Misrecalling temporary or longer-term A learning problem or negative transfer of Acceptable decision or plan formed too late to be Sticking to a faulty plan, belief or interpretation, Mental Block fully effective. perhaps even despite evidence to the contrary. A mental block - just cannot recall information. No decision or no plan Knowledge problem Distraction / Preoccupation No decision made or no plan formed Lacks required knowledge due to training or Momentary distraction or longer-term learning. Decision freeze Decision 'freeze' due to complexity or emotion. More Psychological Categories Collecting human error data ►Action error: in executing action ► Experimental studies Internal Error Mode Internal Error Mechanism ► Expert judgments Action ► Self made error reports Selection error Variability ► Human data recorder Unintended manual selection or positioning. Lack of manual precision, fluency or intonation. Unclear information Confusion ► Automatic data recorder Transmitting or recording unclear, vague or Selecting an object that looks similar to another, is ► Published literature ambiguous information. in a confusable position, or is functionally similar. ► Human error data banks and sources Incorrect information Intrusion Inadvertently transmitting or recording incorrect Thoughts, habits or task interference effects information. cause a controller to do or say something unintended. Distraction / Preoccupation Momentary distraction or longer-term preoccupation. Other slip Other slip of the tongue, pen, action etc.
Human error data banks Detecting Error: TAFEI ►Data store Established in 1962 by American Institute for Research, ► Task Analysis for Error Pittsburgh and it contains estimates for time and human Identification performance ► Model of human interaction ►Operational performance recording and evaluation with products data system ► Consider possible transitions developed to collect data on operational human performance for each state by the US Navy Electronics Laboratory, San Diego ► Ask whether transitions are ►Nuclear plant reliability data system ‘legal’, (needed to fulfil specific goal) ►Aviation safety reporting system developed by NASA and contains information on civil aircraft accidents ►Safety related operator action program ►Technique for establishing personnel performance standards
Error Remediation ►Task Design: perform a Task Analysis identify potential performance bottlenecks (eg, high working memory or attentional loads, stressors, etc) eliminate these bottlenecks by changing the human component of the task ►Equipment Design: minimize perceptual confusion, make components distinctive (bad eg, space shuttle) Design systems to be error-tolerant (feedback, error correction) forcing functions: physical constraints that prevent operators from committing an error (eg, transmission locks) Reminders (eg, “lights are on”) Avoid multi-mode systems ►Train for Errors: during training make sure some errors happen--learn the hard way!