Omission Neglect

Omission Neglect Definition

Omission neglect refers to insensitivity to missing information of all types—including unmentioned or unknown options, alternatives, features, properties, characteristics, possibilities, and events. When people fail to think about what they do not know, they underestimate the importance of missing information, and this leads people to form strong opinions even when the available evidence is weak. This can lead to bad decisions that people later regret.

Omission Neglect History and Background

Omission NeglectIt is often surprisingly difficult to notice that important information is missing. For example, in the story, “The Silver Blaze,” Sherlock Holmes asked Inspector Gregory to consider a curious incident involving a dog. Gregory replied that nothing happened, and Holmes proclaimed, “That was the curious incident.” This clue enabled Holmes to deduce that the culprit must have been someone familiar to the victim’s dog. Most people would miss this important clue because most people, like Gregory, pay little attention to nonevents.

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Other types of omissions are also important. It took scientists hundreds of years to discover the importance of using a control group, or a condition involving the omission or the absence of a cause, in their experiments. In fact, scientists failed to recognize the critical importance of a control group until relatively recently in the history of science (following the publication of A System of Logic by John Stuart Mill in 1848). Even scientists are surprisingly insensitive to the absence of a property, such as the absence of a cause. Similarly, it took early mathematicians thousands of years to discover the crucial concept of zero, the number that represents nothingness or the absence of quantity.

Omission Neglect in Everyday Life

In everyday life, people typically receive limited information about just about everything—such as political candidates, public policies, job applicants, defendants, potential dating partners, business deals, consumer goods and services, health care products, medical procedures, and other important topics. News reports, advertisements, conversations, and other sources of information typically provide only limited information about a topic. When people overlook important missing information, even a little information can seem like a lot. Ideally, people should form stronger beliefs when a large amount of information is available than when only a small amount is available. However, when people are insensitive to omissions, they form strong beliefs regardless of how much or how little is known about a topic. Furthermore, in rare instances in which a large amount of information is available, forgetting occurs over time and insensitivity to information loss from memory, another type of omission, leads people to form stronger beliefs over time.

For example, consumers should form more favorable evaluations of a new camera when the camera performs well on eight attributes rather than only four attributes. However, research shows that consumers form equally favorable evaluations of the camera regardless of how much attribute information was presented. The amount of information presented matters only when consumers were warned that information might be missing. This warning increased sensitivity to omissions and lead consumers to form more favorable evaluations of the camera described by a greater amount of information.

Similar results are observed in inferences, or judgments that go beyond the information given. Consumers received a brief description of a new 10-speed bicycle and were asked to rate its durability even though no information about durability was provided. When consumers inferred durability immediately after reading the description, they realized that no information about durability was presented and they formed moderately favorable inferences about durability. However, when consumers inferred durability one week after reading the description, extremely favorable and confidently held inferences were formed. This result was observed even though memory tests showed that people forgot most of the information that was presented after the one-week delay. Hence, people’s inferences were stronger when they remembered a little than when they remembered a lot. In other words, omission neglect leads people to form less accurate opinions and, at the same time, leads people to hold these opinions with greater confidence.

Why Does Omission Neglect Happen?

Omission neglect occurs for several reasons. First, missing information is not attention drawing: out of sight, out of mind. Second, people often focus on one object at a time rather than comparing many objects. This makes it difficult to determine whether enough information is available. It also makes it difficult to determine how much better or worse one option is relative to another. Third, thinking about presented information can inhibit or prevent people from thinking about nonpresented information.

Fortunately, people are not always insensitive to omissions. People are less likely to overlook missing information when they are highly knowledgeable about a topic or when they are encouraged to compare objects or issues described by different amounts of information. Under these special circumstances, people are less likely to underestimate the importance of missing information, less likely to overestimate the importance of readily available information, and less likely to make bad decisions.

Omission Neglect in Judgments and Decision Making

Although judgments and decisions are often more reasonable when people are sensitive to omissions, people frequently and typically neglect omissions. Research on the feature-positive effect, or the tendency to learn more quickly when a distinguishing feature or symbol (e.g., a letter, number, or geometric figure) is present versus absent, has shown that people find it very difficult to learn that the absence of a feature is informative when people try to categorize a new object.

A fault tree is a list of possible reasons why an object might fail to perform properly, such as why a car will not start. Many people think that a fault tree will help them to determine the cause of a problem more quickly. However, when using fault trees, people typically underestimate the likelihood that an unmentioned alternative could be the cause of a problem. This result is observed regardless of how many or how few alternatives are presented in the fault tree. This result is also similar to previous research results showing that people form strong beliefs regardless of how much or how little is known about a topic.

Missing information is also neglected in the Ellsberg paradox, which is the name given to the fact that people prefer to bet on known probabilities rather than on unknown probabilities. Most people are indifferent between red and black when betting on whether a red or black marble will be drawn from a jar containing 50% red and 50% black marbles. Most people are also indifferent between red and black when betting on whether a red or black marble will be drawn from a jar of red and black marbles with an unknown distribution. When given a choice between the two jars, however, most people prefer to bet on the jar with the 50-50 distribution rather than the jar with the unknown distribution. Hence, making comparisons can help people to notice important omissions and can help people to form better judgments and decisions.

Evolutionary forces may have played a role in the development of omission neglect. The presence of a dangerous predator is a relatively rare event that requires immediate action. However, the absence of a predator is a commonplace event that does not raise a call to action. Because infrequently encountered objects are more informative than frequently encountered objects, it may be more efficient to focus on objects that are encountered rather than not encountered.

People have become accustomed to making judgments and decisions based on whatever information they happen to encounter. Sometimes judgments are based on a relatively large amount of information, and sometimes they are based on a relatively small amount. Regardless of the quality or the quantity of the information that is encountered, omission neglect is common because missing information is not attention drawing, presented information seems more important than it actually is, and presented information interferes with the ability to think about missing information. Frequently, people would be better off if they stopped to think about what they do not know rather than taking whatever information is readily available and running with it.


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