The most common cognitive biases

The cognitive biases are the mistakes that the human mind makes. Far from being minor stumbles, these biases not only represent an obstacle to understanding the reality that surrounds us, but they also greatly influence the way we relate with others. The antidote par excellence is the scientific method but applying it more or less constantly as a filter to our judgments is an undertaking that requires a lot of effort (and humility!).

A first step is to admit that the mind can make mistakes. A second step is to understand how. So here it is a brief description of the most common cognitive bias:

  1. Confirmation bias: tendency to surround oneself with people and to look for information that confirm one’s opinion, ignoring anything that might question one’s beliefs.

Persons believing in extrasensory perception (ESP) will keep close track of instances when they were ‘‘thinking about Mom, and then the phone rang and it was her!’’ Yet they ignore the far more numerous times when (a) they were thinking about Mom and she didn’t call and (b) they weren’t thinking about Mom and she did call. [Goodwin (2010)]

2. Negative bias: tendency to give more attention and weight to negative news than to the positive ones. Although crimes, wars, violence and other injustices have decreased significantly compared to the past, many people keep believing that things are getting worse and worse.

3. Bandwagon effect: tendency to believe/do something because many people believe/do it. Following the mass is much easier than thinking for yourself.

A typical example comes from the politics world: during the 1992 U.S. presidential elections, Morwitz and Pluzinski conducted a study at a North-East university. Some of the 214 economics students were given the results of the national polls that showed Bill Clinton ahead; others were not told about the polls results. The study showed that several students who intended to vote for Bush changed their minds after seeing the outputs of the survey [Morwitz and Pluzinski (1996)].

4. Illusory correlation: tendency to erroneously assume a cause and effect relationship that does not actually exist.

This fallacy of the mind is, for example, the basis of many a-scientific beliefs such as the alleged link between vaccines and autism, meat and cancer, etc. Correlation does not imply a cause-effect relationship, yet many people tend to relate features that are actually independent.

This attitude can be as dangerous as ridiculous:

More barrels of oil, please! (credits)
Margarine is dangerous. For couples. (credits)

Other funny examples of spurious correlation can be found here.

5. Overconfidence effect: tendency to overestimate one’s own abilities with respect to the actual performance or to the others’ performance. For the latter case, a more proper definition is illusory superiority.

This type of mind fallacy is typical of strongly narcissistic personalities and is considered “the most pervasive and potentially catastrophic among the cognitive bias” [The psychology of judgment and decision making, Plous(1993)].


6. Dunning-Kruger effect: tendency of some people not to adequately assess their level of (in-)competence by actually overestimating their knowledge. This lack of awareness is attributed to their low level of competence which deprives them of the ability to critically analyze their performance.

If you are incompetent, you cannot know you are incompetent. The skills needed to produce the right answer are exactly the skills needed to recognize what the right answer is. (Dunning)

One of the most painful things of our time is that those who have certainties are stupid, while those with imagination and understanding are full of doubts and indecisions. (Bertrand Russell)


If you did not recognize yourself in any of these biases, don’t mind, the list is actually much longer. If you still cannot recognize yourself in any bias, then you are most likely affected by the bias blind spot, which is the tendency not to recognize your own bias (which is a bias itself).

📊 Researcher in Geophysics || ✍️ Passionate about writing

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