Peter Carthcart Wason (1960)
2-4-6 Hypothesis Rule Discovery Task
Class Activity
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What Sequences Make Me Happy?
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What Sequences Make Me Happy?
2,4,6
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What Sequences Make Me Happy?
2,4,6

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What Sequences Make Me Happy?
2,4,6

count up by 2’s
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What Sequences Make Me Happy?
2,4,6

count up by 2’s
50%
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What Sequences Make Me Happy?
2,4,6

count up by 2’s
50%
__,__,__
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What Sequences Make Me Happy?
1. Write a 3 number sequence.
2. Wait for me to tell you if it fits my rule , or not .
3. Take your best guess for what my rule is.
4. Estimate your confidence from 0% to 100%
Repeat the steps.
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What Sequences Make Me Happy?
Poll of Our Class:
Guess What Rule Makes Me Happy
N
count up by 2’s
count up by X’s
a formula like (a,b,c) a+b=c
any increasing sequence
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What Sequences Make Me Happy?
2,4,6

count up by 2’s
50%
__,__,__
Any increasing
sequence of numbers.
Why did so many of you
become so confident
about a wrong answer?
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Typical Response
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Typical Response


count up by 2’s
50%
count up by 2’s
60%
count up by 2’s
70%
count up by 2’s
80%
42,44,46



count up by 2’s
90%
96,98,100

count up by 2’s
100%
2,4,6
8,10,12
10,12,14
20,22,24
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Confirmation Bias
We actively try to support what we
already believe rather than trying to
find out where we might be wrong. We
seek out information that confirms our
view. We interpret ambiguous or
mixed information to confirm our
existing theories (e.g., Darley & Gross, 1983).
This confirmation bias is one of the
many natural inclinations we have in
our thinking and decision-making.
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Challenge Confirmation Bias
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Challenge Confirmation Bias
2,4,6
5,10,15
3,7,10
4,25,100
3,20,700
3,2,1
3,1,2
7, ⅓, 12








count up by 2’s
50%
count up by X’s
50%
the first two add to the third
50%
operation combines 1st two for 3rd
50%
any sequence going up
50%
any sequence going up
60%
any sequence going up
70%
any sequence going up
80%
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Confirmation Bias in Everyday Life
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Original Task
The original 2-4-6 Hypothesis Rule Discovery Task was
created by Cognitive Psychologist Peter Cartcart Wason.
Here is the original citation and record sheet.
Wason, P. C. (1960). On the failure to eliminate hypotheses in a conceptual
task. The Quarterly Journal of Experimental Psychology, 12, 129-140.
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About this Class Activity
The original adaptation for this class activity was created by Kevin Grobman in
2001 and was published on DevPsy.org in 2003. Over the years I polished the
handout and slides, as well as improved the clarity with which I share it with
other teachers. This page was revised with these improvements in 2017. In
2018 the American Psychological Association (APA) Society for the Teaching of
Psychology (STP) included it in an ebook of lab activities for high school
Psychology classes.
This is one of many activities for the teaching and learning of Psychology
available at http://www.DevPsy.org and http://www.PerplexingQuestions.org
Please use the following citation for these slides, the handout, and this activity:
Grobman, K. H. (2003). Confirmation Bias: A class activity adapted from
Wason’s 2-4-6 Hypothesis Rule Discovery Task. Retrieved from:
http://www.DevPsy.org/teaching/method/confirmation_bias.html
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