In-class Experiments #6 : Hindsight, False Consensus & Confirmation Biases

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To continue the in-class experiments series, I ran three more inclass experiments in the recent summer course I gave – Hindsight Bias, False Consensus Bias & Confirmation Bias.

The three are relatively straightforward and can be combined into a single handout.


[UPDATE September 2018: All teaching materials now shared on the teaching page]


Hindsight Bias

Hindsight Bias The “I knew it all along” effect, where people being confronted with a fact tend to construe a belief that they actually knew it is or would be so all along.

The handout includes two versions (without the bold highlight):

  • Version A – Researchers have found that people with low self-confidence are more susceptible to flattery than those with high self-confidence. In a sentence or two, why do you think this is true?
  • Version B – Researchers have found that people with high self-confidence are more susceptible to flattery than those with low self-confidence. In a sentence or two, why do you think this is true?

So, as you can see that these two findings are contradictory to one another. The students are asked to write down why they believe this to be true and then indicate the extent to which they found this finding surprising or predictable.

In our class, 20 out of the 25 students who received version A and 19 out of the 26 students who received version B found their version of the findings unsurprising and predictable. Meaning, that no matter what the finding was, the students has the impression that they ‘knew it all along’.


The False Consensus Bias

The False Consensus BiasPeople generally tend to view their opinions as being that of the consensus.

For this in-class experiment I constructed a few Hong Kong relevant questions that I thought would be strongly disputed among the students.

I included the following items :

  1. Leung Chun-Ying is a good Chief Executive for Hong Kong
  2. Hong Kong is a part of China
  3. Taiwan is a part of China
  4. HKUST is the best university in HK
  5. Burger King is better than McDonalds’
  6. Japanese food is more delicious than Korean food


For each of those items I asked the students to indicate :

  • Whether they agree or disagree with the statement.
  • Their estimation of the percentage of students in class who share their views regarding the statement.


Some of the statements indeed confirm the false consensus bias.

For example :


Even among the 13.5% of the students who disagreed with the statement, their average estimation of the percentage of the other students who share their disagreement was 72%.

Let’s see another one :



The 34% of the students who disagreed with the statements thought on average that 78% of the other students shared their disagreement. In both the Taiwan and Hong Kong statements it seems like the false consensus bias was very strong.

Two of the statements didn’t work as strongly but they were still in the right direction, and the message to the students was quite clear.


Confirmation Bias

Confirmation BiasLast, the confirmation bias. This one is a bit more tricky, since it relates to find support for preconceived perceptions and beliefs. A very simple demonstration, if not too simple, is the following. Two versions of a question:

  • Are you happy with your social life?
  • Are you UNhappy with your social life?

and the following choices :

  • Yes
  • No
  • Undecided


To their amazement, students realize that the majority of people answer “yes” to both of those questions in a random assignment between-subject design. People conclude a search for evidence as soon as they find information that supports the affirmative answer.



So, what to make of all of this. Ask your students!

When confronted with the the biases, the follow-up debates focused on :

  1. Why does this bias occur?
  2. How does this bias apply to our everyday life
  3. How does this bias apply to organizational life
  4. How might one overcome this bias?
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