The human mind is a very powerful problem-solving machine capable of finding the "deep structure" of a problem (in KB-performance). In explaining the concept of deep structure, Dr. Schank (1982) refers to the similar themes of Romeo and Juliet and West Side Story. These are two very different stories, one about Renaissance Italy, the other about gang warfare In modern New York. But on a deeper level, they share the same structure. To discover this similarity, however, a person must mentally summarize the plot lines and compare them - a KB-performance activity. KB-performance uses an enormous amount of mental resources, is slow, and happens in sequence (as opposed to RB-performance, were many RB rules might be active at one time). Perhaps even more frequently than with RB performance, people make mistakes while in KB-performance. For ease of organization, these mistakes can be organized into two categories: bias and heuristics.

　

A Heuristic is a mental "rule of thumb." People often resort to the use of heuristics (mental rules of thumb) that help them to diagnose problems without expending too much mental effort and thus too much time. Often, these heuristics serve them well; however, they are shortcuts and as such mariners may be shortchanging themselves of adequate and accurate information. Rather than processing all available information and following reasoning to its most probable and logical end, taking of a shortcut may give a person a false understanding of the actual situation. This section discusses some common heuristic mistakes. The classifications below the level of 'heuristics' are required ONLY in formal investigations.

　

VII.D.2.a.i. Representative Heuristic (required only for Formal investigations)

Definition: "This is the tendency to match cues drawn from a current situation to those that form a mental representation of a particular situation that already exits in long-term memory. Simply stated, a comparison is made between perceived information and what exists in memory. If it is decided that the cues of the current situation match those of a particular situation stored in memory, then the conclusion drawn is that the situations are similar or the same. In turn, it follows that the decision-maker may conclude the actions taken previously are appropriate again. However if the cues perceived from the current situation were not complete or were ambiguous, an incorrect match could occur. Should the pattern of cues in long-term memory not be a good indicator of the current situation, the person's judgment and decision-making could be faulty. Once a match has been established, people tend to cling to that interpretation, often not changing it despite evidence to the contrary. [Reason: 86-96]

Example: When receiving directions on how to find a specific location in a city that you have visited on a few occasions, your attention may focus on only those street names and landmarks that sound familiar to you. A mental map of your route would be recalled from memory. Since you did not consider the other directional cues, your mental map was probably incorrect for this situation, which most likely resulted in your getting lost.

Summary; The defining characteristics of a representative heuristic error include: i) perceived information is incorrectly matched with specific patterns stored in memory; and ii) current actions taken are incorrect because they are based on the wrong interpretations of the current situation.

　

VII.D.2.a.ii. Availability Heuristic (required only for Formal investigations)

Definition: "This is the tendency to diagnose a situation using the hypothesis most available in memory, i.e. giving undue weight to facts that come readily to mind. The most available hypothesis may not be the most probable, but simply the most recently experienced or less complicated one." [Reason: 86-96]

Example: In the "Human Factors in Investigations" course, Maury Hill (Chief; Human Performance Division) shows a slide with a pattern of lines and asks the course participants to guess what the pattern was or represented. After a short while, he informed the class that the pattern was a map of a coastal area. When the next slide was given and the same question asked, the majority of the participants "saw" the pattern of lines in terms of another map. As it turned out, the pattern was an outline drawing of a cow's head.

Summary: The defining characteristic of an availability heuristic error is that an inappropriate hypothesis is selected because of its convenience.

　

VII.D.2.a.iii. "As if" Heuristic (required only for Formal investigations)

Definition: "This the tendency to treat all information sources "as if" they were of equal reliability. Information that is at best marginal is given the same degree of reliability as that which is very reliable." [Reason: 86-96]

Example: A simple method to measure one's heart or pulse rate is to press lightly with two fingers on a blood vessel located near the skin's surface, such as at the wrist or throat, and count the pulses (i.e. surges of blood as the heart pumps). The reliability of this method can be significantly lower than that found with other methods, such as listening for the beating sound with a stethoscope at the chest level or use of an electrocardiogram machine to measure the electrical activity of the heart. For a general description of the heart function, the wrist or throat palpation may be given similar weighting of reliability to provide adequate information. However in critical situations the output of an electrocardiogram should be used as the measure of heart function.

Summary: The defining characteristic of an "as if' heuristic error is that all perceived information is incorrectly given the same weight with regard to reliability.

　

A Bias is the tendency to apply a certain response regardless of the situation. Biases are fundamentally problems with how a person perceives the "problem space," and what factors they choose to pay attention to. This section describes some of the more common bias mistakes. The classifications below the level of 'bias' are required ONLY in formal investigations.

　

VII.D.2.b.i. Salience Bias (required only for Formal investigations)

Definition: "This is the tendency to focus on physically important characteristics or evidence (e.g. loud, bright, recent, centrally visible, easy to interpret) and ignore critical cues that might provide diagnostic information about the nature of a problem. Salience bias results from the fact that decision-makers do not necessarily process all information available to them, particularly under times of stress. This bias is also known as " selectivity" due to the selective information processing by a decision-maker." [Reason: 86-96]

Example: Prior to loading a tank barge on the rivers, its tanks were cleaned and workers drained a tank containing residual methanol. The residual methanol was apparently drained to the bow rake, which also served as the cargo pump room. Five days later crewmen visually identified "water" in the bow rake during a compartment check just before loading. Methanol is a colorless liquid resembling water, and it is possible that prevailing conditions precluded the crewmen from smelling the noxious vapors. A careless cigarette butt later caused a major explosion in the space.

Summary: The defining characteristic of a salience bias error is that attention is either given to the wrong characteristics or not given to the right characteristics.

　

VII.D.2.b.ii. Confirmation Bias (required only for Formal investigations)

Definition: "This is the tendency to seek information that will confirm what we already believe to be true. Information that is inconsistent with the chosen hypothesis is then ignored or discounted." [Reason 86-96]

Example: A Master was observing a crossing from the starboard bridge wing after having looked at the situation on the ARPA. While looking on the ARPA, the Master concluded that his vessel would pass well ahead of the crossing vessel to his starboard. Once on the bridge wing, he took bearings to the incoming vessel and observed her lights through his binoculars, but failed to note that due to course changes the two vessels were on a "constant bearing - decreasing range" (CBDR). Until just before the collision, he continued to believe his vessel would pass ahead of the other. The vessels collided nearly where the Master was standing.

Summary: The defining characteristic of a confirmation bias error is that attention is only given to information that supports a previously chosen hypothesis.

　

VII.D.2.b.iii. Framing Bias (required only for Formal investigations)

Definition: "In risky decision-making, there is a tendency to frame the problem as a choice between gains or between losses. With respect to losses, people are biased to choose the risky loss which is less probable although more disastrous, rather than the certain loss." [Reason: 86-96]

Example: When returning to Canada from a visit to a foreign country, many people choose not to declare certain items requiring the payment of duty. If initially claimed, there will be a known cost (certain loss). If one is caught without claiming the items, the unknown cost (risky loss) could be much greater, but is considered less likely to occur.

Summary: The defining characteristics of a framing error are: i) alternatives are rated in terms of losses (or gains); and ii) given the choice between a sure loss versus an uncertain probability of disaster, people are biased toward the risky choice.

　

VII.D.2.b.iv. Overconfidence Bias (required only for Formal investigations)

Definition: "There is a tendency for people to overestimate the correctness of their knowledge of the situation and its outcome. The result is that attention is placed only on information that supports their choice and ignores contradictory evidence." [Reason: 86-96]

Example: Inexperienced staff who have just received preliminary job-related training can sometimes fall prey to this bias when attempting to apply their newly attained knowledge. Without the tempering afforded by on-the job experiences, an individual may overrate the utility of "classroom" theory versus the more "work-shop"- oriented knowledge used by peers.

Summary: The defining characteristic of an overconfidence error is that attention is given to certain information because an individual overrates his/her knowledge of the situation.