The skill-based performance involves highly practiced, primarily physical actions in very familiar situations in which there is little conscious monitoring. Such actions are usually executed from memory without significant conscious thought or attention. Behavior is governed by preprogrammed instructions developed by either training or experience and is less dependent upon external conditions. Information that can be processed with little or no allocation of attention resources is called automatic processing. When skills are learned to the point of being automatic, the working memory load is typically reduced by 90%. This occurs after extensive practice of a task so that it can be performed “without thought.” Many actions in a typical day are controlled unconsciously by human instinct, such as keyboarding, writing one’s signature, taking a shower, and driving a car. In the skill-based mode, the individual is able to function very effectively by using pre-programmed sequences of behavior that do not require much conscious control. It is only occasionally necessary to check progress at particular points when operating in this mode.
Examples of skill-based activities for well-trained and practiced individuals include:
- mowing the lawn;
- using a hammer or other hand tool;
- controlling various processes manually (such as pressure and level),
- hanging a tag;
- analyzing chemical composition of a routine sample;
- performing repetitive calculations;
- using measure and test equipment;
- opening a valve;
- taking logs; and
- replacing parts during maintenance
Error Modes are the prevalent ways, not the only ways; people err for the particular performance mode. Error modes are generalities that aid in anticipating and managing error-like situations aggravated by inattention, misinterpretation, and inaccurate mental models.
Skill-Based Error Mode – Inattention
The error mode for skill-based performance is inattention. Skill-based errors are primarily execution errors involving action slips and lapses in attention or concentration. Errors involve inadvertent slips and unintentional omissions triggered by simple human variability or by not recognizing changes (note the Δ symbol on the above chart) in task requirements, system response, or facility conditions related to the task. Some examples of errors committed while in the skill-based performance level follow.
- When addressing an envelope, he put his old address in the return box instead of his new (correct) address.
- She forgot to drop off shoes at the shoe shop to be repaired and instead drove right past the shoe shop and straight to her home.
- An electrician had been asked to change a light bulb that indicated whether a hydraulic on/off switch was selected. The hydraulic system was being worked on, and the electrician was aware that it would be unsafe to activate the system. Nevertheless, after changing the bulb, and before he had realized what he was doing, he had followed his usual routine and pushed the switch to the ”on” position to test whether the light was now working.
- Intending to shut down lines A and B, the operator pressed the “shut-off’“ control buttons for lines C and D.
Under ideal conditions, the chance for error is less than 1 in 10,000, according to a study in the nuclear power industry.
People often possess an accurate understanding of the task and have correct intentions. Roughly 90% of a person’s daily activities are spent in the skill-based performance mode. However, only 25% of all errors are attributable to skill-based errors in the nuclear power industry. Potentially, a person can be so focused on a skill-based task that important information in the workplace is not detected. Another concern for skill-based tasks is that people are familiar with the task. The greater the familiarity, the less likely the perceived risk will match the actual risk. People become comfortable with risk and eventually grow insensitive to hazards. Several tools are designed to help anticipate, prevent or catch skill-based errors ( task preview, job-site review, questioning attitude, stop when unsure, self-checking, pre-job briefing, place-keeping, peer check, and concurrent verification)
Rule-Based Performance
People switch to the rule-based performance level when they notice a need to modify their largely pre-programmed behavior because they have to take account of some change in the situation. The work situation has changed such that the previous activity (skill) no longer applies. This problem is likely to be one they have encountered, been trained to deal with, or covered by the procedures. It is called the rule-based level because people apply memorized or written rules. These rules may have been learned as a result of interaction with the facility, through formal training, or by working with experienced workers.
The level of conscious control is between the knowledge- and skill-based modes. The rule-based level follows an IF (symptom X), THEN (situation Y) logic. In applying these rules, we operate by automatically matching the signs and symptoms of the problem to some stored knowledge structure. So, typically, when the appropriate rule is applied, the worker exhibits pre-packaged units of behavior. He/she may then use conscious thinking to verify whether or not this solution is appropriate.
The rule-based performance aims to improve one’s interpretation of the work situation so that the appropriate response is selected and used. This is why procedures are prepared for situations that can be anticipated. Procedures are pre-determined solutions to possible work situations that require specific responses. Rules are necessary for those less familiar, less practiced work activities for which a particular person or group is not highly skilled. Not all activities guided by a procedure are necessarily rule-based performances. In normal work situations, such activities are commonly skill-based for the experienced user.
Examples of rule-based activities include:
- deciding whether to replace a ball bearing inspected during preventive maintenance;
- responding to a control board alarm;
- estimating the change in tank level based on a temperature change (thumb rules);
- feeling equipment for excessive vibration or temperature on operator rounds;
- performing radiological surveys;
- using emergency operating procedures; and
- developing work packages and procedures
Rule-Based Error Mode
Since rule-based activities require interpretation using an if-then logic, the prevalent error mode is a misinterpretation. People may not fully understand or detect the equipment or facility conditions calling for a particular response. Errors involve deviating from an approved procedure, applying the wrong response to a work situation, or applying the correct procedure to the wrong situation. Examples of errors committed when working in the rule-based performance level include the following.
A driver was about to pull out into the traffic flow following a stop at the side of the road. He checked the side-view mirror and saw a small green car approaching. He briefly checked his rear-view mirror (which generally gives a more realistic impression of distance) and noted a small green car some distance away. He then pulled out from the shoulder of the road and was nearly hit by a small green car. There were two of them, one behind the other. The driver assumed they were one and the same car. The first car had been positioned so that it was only visible in the side-view mirror.
The technician knew that normal tire pressure in automobile tires is 32-35 psi. So, when he was required for the first time to air up a smaller, temporary-use automobile tire, he filled the tire to the customary 35 lbs. In actuality, small-diameter, temporary-use tires are aired up to 55-60 psi.
A northbound commuter train in London in 1988 ran into a stationary train’s back after passing a green signal. Thirty-five people died, and 500 were injured. The signal light had given the wrong signal because the old signal wires had come into contact with nearby equipment for the new signal system that causing a wrong-side signal failure. The light should have shown red for stop. The electrician who had wired the signal on the new system just the day before the accident had never been properly trained. He failed to cut off or tie back and then insulate old wires as he wired in the new signal system. He merely bent old wires back out of the way. The untrained technician had learned bad habits on his own that became his “strong but wrong rules.” His application of a bad rule went uncorrected.
The chance for error increases when people make choices or decisions, especially in the field. Rule-based and knowledge-based performance modes involve making choices. Less familiarity with the activity increases the chance for error to roughly 1 in 1,000. In terms of reliability, this is still very good (99.9%). Studies have shown that roughly 60% of errors in the nuclear power industry are rule-based.
Some tools to help anticipate, prevent, or catch rule-based errors. They include task preview, procedure adherence, pre-job briefing, questioning attitude, peer-checking, and concurrent verification.
Knowledge-Based Performance
Warning: the terminology of knowledge-based performance can be confusing! It is tempting to think that much of the engineering design work and the scientific investigations and research falls in the knowledge-based category – simply because highly knowledgeable people perform such work. However, we must avoid the temptation to shrug off the essential nuances and simply argue that since we do research or one-of-a-kind work, and our people are highly educated and skilled, then our work is knowledge-based. The truth is quite the opposite. The situation described as “knowledge-based mode” might better be called “lack of knowledge” mode.
As defined by Rasmussen, knowledge-based work generally means that we don’t really understand what we are doing. Even in the most cutting-edge science, the ability to develop and conduct controlled experiments depends on control, keeping the uncontrolled variables as few as possible so that we may observe the results of the experiment in order to hypothesize, test theories, and ultimately develop new knowledge. It might be argued that the accomplished researcher has highly refined abilities to work in skill and rule modes to work in knowledge mode since working in knowledge mode is so difficult.
Not all hazards, dangers, and possible scenarios can be anticipated in order to develop appropriate procedures. Even training is unable to anticipate all possible situations that can be encountered. There are some situations in which no procedure guidance exists, and no skill applies. Dr. James Reason concludes that the knowledge-based level of performance is something we come to very reluctantly. Humans only resort to the slow and effortful business of thinking things through on the spot after they have repeatedly failed to find some pre-existing solution.
Hence, knowledge-based behavior is a response to an unfamiliar situation (no skill or rule is recognizable to the individual The person must rely on his or her prior understanding and knowledge, their perceptions of present circumstances, similarities of the present situation, and similarities to circumstances encountered before, and the scientific principles and fundamental theory related to the perceived situation at hand. People enter a knowledge-based situation when they realize they are uncertain about what to do. If uncertainty is high, then the need for information becomes paramount. Our attention must become more focused to gain information about what we are doing or about to do.
Knowledge-based situations are puzzling and unusual to the individual. Often our understanding of the problem is patchy, inaccurate, or both. In many cases, information sources contain conflicting data, too much data, or not enough data, amplifying the difficulty of problem-solving. Additionally, consciousness is very limited in its capacity to hold information, storing no more than two or three distinct items at a time. Consciousness tends to behave like a leaky sieve, allowing things to be lost as we turn our attention from one aspect of the problem to another. Because uncertainty is high, knowledge-based tasks are usually stressful situations.
Knowledge-based activities involve problem-solving. Such situations require the use of fundamental knowledge of processes, systems, and so on—“thinking on your feet.” Examples of common problem-solving situations include the following:
- troubleshooting;
- performing an engineering evaluation of a new design;
- reviewing a procedure for ‘intent of change;’
- resolving conflicting control board indications;
- holding meetings to address problems;
- conducting scientific experiments;
- resolving human performance problems;
- planning business strategies, goals, and objectives;
- performing root cause analysis of events;
- conducting trend analyses;
- designing equipment modifications;
- making budget allocation decisions
- allocating resources;
- changing policies and expectations; and
- performing an engineering calculation
Knowledge-Based Error Mode
Knowledge-based activities require diagnosis and problem-solving. Considerable demands on the information-processing capabilities of the individual are necessary when a situation has to be evaluated from the first principles. It is not surprising that humans do not perform very well in high-stress, unfamiliar situations where they are required to “think on their feet” in the absence of rules, routines, and procedures to handle the situation. People tend to use only readily available information to evaluate the situation. Also, problem solvers often become over-confident in the correctness of their knowledge, an “I know I’m right” effect. They also become enmeshed in one aspect of the problem to the exclusion of all other considerations. Decision-making is erroneous if problem-solving is based on inaccurate information. Often, decisions are made with limited information and faulty assumptions.
Consequently, the prevalent error mode is an inaccurate mental model of the system, process, or facility status. Under such circumstances, the chance for error is particularly high, approximately one in two (50 percent) to one in ten. Studies indicate that roughly 15% of all errors are knowledge-based. Several tools help anticipate, prevent, or catch knowledge-based errors. They include, for example, technical task pre-job briefing, project planning, problem-solving, decision-making, and peer review.
How Performance Modes Can be Used
A better contextual understanding of individuals’ conscious and automatic behaviors as described in the skill, rule, and knowledge performance modes, and knowing the kinds of errors individuals tend to make while working in those various modes, can be extremely useful. Managers responsible for establishing and maintaining effective controls can use this information well. Workers need accurate, complete, and unambiguous procedures and guides for reference when doing rule-based work. They may also need access to a subject matter expert when making choices about the rules to select and for the correct application.
Workers performing skill-based work need adequate tools to minimize action slips. They need to be free from interruptions and distractions that aggravate concentration, divide their attention, and contribute to lapses in memory that cause an error. Workers may benefit from simple job aids and reminders in skill-based performance mode. On the other hand, for individuals working in the knowledge-based mode, where their understanding of the problem is often patchy, inaccurate, or both, and where the slow and effortful business of thinking things through is needed, collaboration with a small team of thoughtful, committed, and experienced individuals is needed to help in problem-solving and decision-making. Individuals performing work in any of the performance modes can benefit from the use of the error-reduction tools addressed later in this chapter.
When errors and mistakes of consequence occur, that indicates some corrective action is needed to minimize recurrence; knowing the work processing method or performance mode the individual was working in is instructive. Often, workers involved in skill-based performance who err are scheduled for retraining as a logical solution. But, retraining workers to do work that is already basically memorized and automatic, performed with little conscious thought because of the nature of the work, is a waste of time and is an insult to the worker. It is very hard to train a worker not to repeat something he or she did not intend to do in the first place. Training is not the solution in these instances. Observations of work can be very beneficial. People don’t always know why something went wrong.
Observations are used to gather data about worker behaviors, job-site conditions, and organizational support that may have been desired. Inadequate tools, incomplete work packages, scheduling conflicts, poorly written procedures, excessive noise, extreme heat or cold, poor lighting, and so on may contribute to poor performance. Some one-on-one time with the individual may be in order. The purpose is to learn of the circumstances surrounding the slip, trip, or lapse and what, if anything, can be changed in the work environment or with the individual to eliminate a similar reoccurrence. The error may have been provoked by fatigue and stress; the worker may have lost sleep worrying about a teenager who left home. It may be that the worker has become complacent and careless. Distractions and interruptions may have disrupted the worker’s concentration, leading to the error. Those conditions can be controlled, and errors that occur when working in rule-based performance may be corrected through retraining.
Generally, the worker has misinterpreted a requirement or a “rule.” He or she has applied a bad rule to a given application or, conversely, has used a good rule in a wrong application. In these instances, understanding requirements and knowing where and under what circumstances those requirements apply is cognitive in nature and must be learned or acquired in some way. Rule-based errors can be caught or mitigated by individuals exhibiting a questioning attitude, calling a time out, or stopping work when unsure. Peer checks can also stop someone from committing a consequential error.
Corrective action to reduce knowledge-based mistakes is more complicated. An analysis of what went wrong will need to be carried out to formulate a corrective action. It may be that the person’s understanding and knowledge of the system and the scientific principles and fundamental theory related to the system were inadequate. Training or retraining could help. It may be that people’s technical knowledge was adequate, but the three individuals working on the problem lacked problem-solving skills, fell victim to team errors, or failed to communicate with each other to solve the problem effectively. Perhaps the team could not make good decisions in an emergency. Coaching is a proactive solution to helping individuals eliminate errors when working in any performance mode but it is particularly adept for knowledge-based performance modes. Peer evaluations are also effective in this instance.