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.

History and Background

It 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.

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 [Page 634]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.

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