The Fallacy of Positive Instances vs The Overestimation Effect

What is the fallacy of positive instances and examples? 

The fallacy of positive instances is the tendency to remember uncommon events that seem to confirm our beliefs and to forget events that disconfirm our beliefs. Often, the occurrence is really nothing more than coincidence. 

The Fallacy of Positive Instances vs The Overestimation Effect
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The fallacy of positive instances psychology example

For example, you find yourself thinking of an old friend. A few moments later, the phone rings and it’s him. You remember this seemingly telepathic event, but forget all the times that you’ve thought of your old friend and he did not call. In other words, you remember the positive instance but fail to notice the negative instances when the anticipated event did not occur (Gilovich, 1997).

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What is the Overestimation Effect?

The tendency to overestimate the rarity of events is referred to as the overestimation effect. 

The Overestimation effect psychology example 

Suppose a “psychic” comes to your class of 23 students. Using his psychic abilities, the visitor “senses” that two people in the class were born on the same day. A quick survey finds that, indeed, two people share the same month and day of birth. This is pretty impressive evidence of clairvoyance, right? After all, what are the odds that two people in a class of 23 would have the same birthday?

When we perform this “psychic” demonstration in class, our students usually estimate that it is very unlikely that 2 people in a class of 23 will share a birthday. In reality, the odds are 1 in 2, or 50–50 (Martin, 1998). Our students’ overestimation of the rarity of this event is an example of the overestimation effect.


Hockenbury, D. H., & Hockenbury, S. E. (2010). Psychology. New York, NY: Worth Publishers.

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