Skill-based errors

Skill-based Errors manual variability strong but wrong action sequences Train for physical and manipulative skills (repeated practice and feedback) Checklists setting out starting and finishing activities and checks Layout and labeling of controls and process lines Distinguish tetween plant areas with similar appearance but different functions Provide feedback... 

Skill-based errors were associated with almost 47% of unsafe acts, followed by decision errors (33%), routine violations (8%) and perceptual errors (5%). The remaining unsafe acts related to exceptional violations and totaled 7%. 

Pilot failed to Skill based error Procedural Not known... 

Slips and lapses are examples of skill-based errors. A slip can be defined as a failure of attention, in which an action may not be completed as intended. A lapse can be defined as a failure of memory, where an intended action is forgotten and not carried out. This may be due to the operator being intermpted at their task. 

Human Error Skill-based errors Slips of action... 

Skill-based Errors Driver fails to attend or notice critical information, because his mental resources were focused elsewhere, misordering of steps in procedures, the manner or the technique one uses when driving a vehicle. 

The classification of human error within the FASGEP project takes into account the woric of Rasmussen, specifically the classification of Rule-Based errors, Skill-Based errors, and Knowledge-Based errors. The causal relationships for each of the classifications have been developed into a causal network. A type of graphical probability model is based on this. 

Skill-based errors are identified by problems due to inattention or over attention to the q)ecific task. These are typically identified by slips, omissions or repetitions in the product being produced. The causal net for skill-based errors uses attributes of ability, motivation and environment quality (see figure 1). 

Cognitive stage Skill-based error Rasmussen et al.. 

Operator acts. This classification contained 12 contributing factors that were further divided into three groups decision errors, skilled-based errors, and a routine contravention. 

Skill-based behaviours depend mostly on the operator s practice in performing the task. In short the operator can perform the task without ambiguity. A simplistic view is that skill-based errors are slips or hrpses. These errors tend to be related to highly routine activities in familiar circumstances omissions, repetitions, reversals, interference errors and double-capture slips. An example is incorrect use of foot pedal controls of fork-lift trucks. Some fork-lift trucks... 

In the skill-based mode, recovery is usually rapid and efficient, because the individual will be aware of the expected outcome of his or her actions and will therefore get early feedback with regard to any slips that have occurred that may have prevented this outcome being achieved. This emphasizes the role of feedback as a critical aspect of error recovery. In the case of mistakes, the mistaken intention tends to be very resistant to disconfirming evidence. People tend to ignore feedback information that does not support their expectations of the situation, which is illustrated by case study 1.14. This is the basis of the commonly observed "mindset" syndrome. 

The lighter arrows represent typical shortcuts, which omit particular stages in the information-processing chain. These shortcuts may be "legitimate," and would only lead to errors in certain cases. For example, the worker may erroneously believe that he or she recognizes a pattern of indicators and may immediately execute a skill-based response, instead of moving to the rule-based level to apply an explicit diagnostic rule. 

The dotted lines in the diagram indicate the various feedback paths that exist to enable the individual to identify if a particular stage of the processing chain was executed correctly. Thus, if the operating team had planned a strategy to handle a complex plant problem, they would eventually obtain feedback with regard to whether or not the plan was successful. Similar feedback loops exist at the rule and skill-based levels, and indicate opportunities for error correction. The application of the stepladder model to a process industry example is given in Appendix 2A at the end of this chapter. 

The practical implications of this experiment are that when evaluating the effects of shift work due to circadian effects, the type of task being carried out by the worker must be taken into account. For example, skill-based tasks would be expected to exhibit the performance changes characteristic of low memory load tasks, whereas performance variations in knowledge-based tasks would be expected to follow the pattern of high memory load tasks. Performance on rule-based tasks may depend on the degree of frequency of use of the rules, which in turn may determine the memory load. If these results were confirmed by further process plant studies, it would have implications for when different types of operation (involving different levels of memory load) should be scheduled to reduce circadian rhythm effects and minimize errors. 

Advocates of the global approach would argue that human activities are essentially goal-directed (the cognitive view expressed in Chapter 2), and that this cannot be captured by a simple decomposition of a task into its elements. They also state that if an intention is correct (on the basis of an appropriate diagnosis of a situation), then errors of omission in skill-based actions are imlikely, because feedback will constantly provide a comparison between the expected and actual results of the task. From this perspective, the focus would be on the reliability of the cognitive rather than the action elements of the task. 

Slips Errors in which the intention is correct but failure occurs when carrying out the activity required. Slips occur at the skill-based level of information processing. 

Skill-based (S-B) errors are not easily prevented because of the highly automatic (or unconscious) open-loop character of this level of behaviour either you learn to live with them, or you change the task environment in which they occur, when human error seems to have been built in (quite predictably) in the design stage. Especially ergonomics may contribute in... 

Mistakes are errors of systematic decision making and occur when we initiate the wrong action but believing it to be correct - essentially this is the failure of planning [9]. We make mistakes when we undertake tasks which are less familiar and require more cognitive effort than for skill-based activities. Often the behaviour is a result of us being overburdened with matters competing for our attention. 

Skills, rules, and knowledge model Models human information processing in terms of three levels of behavioral control skill based, rule based, and knowledge based Models the processes and requirements for each level of behavior Can be used with quantitative models of human performance to estimate task time and errors... 

Many of these errors occur because the boundary between skill-based and rule-based activity has not been correctly respected. 

Reason divided error into slips, or lapses, and mistakes. Slips or lapses involve the correct choice of a method to achieve a task, but a failure to carry it out correctly. Mistakes on the other hand involve a flaw in the plan which means that even if it is carried out correctly, the objective isn t achieved. Slips and lapses are often skill-and rale-based errors, whereas mistakes are often knowledge-based errors. 

As we have just done, people often talk of breaches or violations of procedures. But it needs to be borne in mind, as noted in Chapter 11 that there are three types of error according to Rasmussen (see Further Reading at the end of this chapter) - skill-based, rale-based and knowledge-based (s, r and k) and so the reasons for the breaches of procedure can be quite different. As an example, we tend to use skill-based and rule-based decisions a thousand times more than knowledge-based decisions in driving a car. 

The attractiveness of systems and engineering approaches in reducing safety incidents has unfortunately not eUminated individual behaviour as the most frequently reported cause. An analysis by Endsley (1999), that most human error incidents resulted from a loss of situational awareness (SA) rather than judgement or skill based decisions, emphasized the importance of attention recovery mechanisms for safety critical roles. Marty papers have been published dealing with attention recovery and fatigue countermeasures to date, however, none have been found that include a mechanism to enable instantaneous and cued recovery at the moment of demand. This chapter formalizes a practice based approach to recovery of SA delivered in over 20 years of counselling and coaching performance with a diversity of clients. 

Other authors like Jens Rasmussen ([14], [15]) distinguish between different levels of human performance and correlate them to required attention and familiarity with the task, cf. Fig.5. It is evident that knowledge-based actions are associated with the highest error probability, but most actions required from a car driver are rule based like obeying traffic signs, or skill-based like changing the gears. 

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