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Rationality
Alan Kaylor Cline
Department of Computer Sciences
The University of Texas at Austin
Based upon classic decision puzzlers
collected by Gretchen Chapman of Rutgers University
1. Sunk Cost:
Group A is told:
As the president of a large pharmaceutical company, you
have invested 10 million dollars of the company's money into
a research project. The purpose was to develop a vaccine
that would prevent people from acquiring HIV. When the
project is 90% completed, another firm begins marketing a
vaccine that prevents HIV infection. Also, it is apparent that
their vaccine is more effective and less expensive than the
vaccine your company is developing. The question is:
should you invest the last 1 million dollars of your research
funds to finish your HIV vaccine?
1. Sunk Cost:
Group A is told:
As the president of a large pharmaceutical company, you
have invested 10 million dollars of the company's money
into a research project. The purpose was to develop a
vaccine that would prevent people from acquiring HIV.
When the project is 90% completed, another firm begins
marketing a vaccine that prevents HIV infection. Also, it is
apparent that their vaccine is more effective and less
expensive than the vaccine your company is developing.
The question is: should you invest the last 1 million dollars
of your research funds to finish your HIV vaccine?
The results are: Yes (85%) and No (15%)
1. Sunk Cost:
Group B is told:
As the president of a large pharmaceutical company, you
have received a suggestion from one of your employees.
The suggestion is to use the last 1 million dollars of your
research funds to develop a vaccine that would prevent
people from acquiring HIV. However, another firm has just
begun marketing a vaccine that prevents HIV infection.
Also, it is apparent that their vaccine is more effective and
less expensive than the vaccine your company could
develop. The question is: should you invest the last 1
million dollars of your research funds to develop the
proposed HIV vaccine?
1. Sunk Cost:
Group B is told:
As the president of a large pharmaceutical company, you
have received a suggestion from one of your employees.
The suggestion is to use the last 1 million dollars of your
research funds to develop a vaccine that would prevent
people from acquiring HIV. However, another firm has just
begun marketing a vaccine that prevents HIV infection.
Also, it is apparent that their vaccine is more effective and
less expensive than the vaccine your company could
develop. The question is: should you invest the last 1
million dollars of your research funds to develop the
proposed HIV vaccine?
The results are: Yes (17%) and No (83%)
1. Sunk Cost:
For Group A the results are: Yes (85%) and No (15%)
For Group B the results are: Yes (17%) and No (83%)
But the situation for A is almost identical to that for B
1. Sunk Cost:
For Group A the results are: Yes (85%) and No (15%)
For Group B the results are: Yes (17%) and No (83%)
But the situation for A is almost identical to that for B
For more info., see: Arkes, H.R. & Blumer, C. (1985).
The psychology of sunk cost. OBHDP, 35, 124-140.
2. Conjunction Fallacy:
A health survey was conducted in a representative sample of adult males in
Chicago of all ages and occupations. Mr. F was included in the sample. He was
selected by random chance from the list of participants.
Please rank the following statements in terms of which is most likely to be true of
Mr. F. (1=more likely to be true, 6=least likely)
1. ____
2. ____
3. ____
4. ____
5. ____
6. ____
Mr. F smokes more than 1 cigarette per day on average.
Mr. F has had one or more heart attacks.
Mr. F had a flu shot this year.
Mr. F eats red meat at least once per week.
Mr. F has had one or more heart attacks and he is over 55 years old.
Mr. F never flosses his teeth.
2. Conjunction Fallacy:
A health survey was conducted in a representative sample of adult males in
Chicago of all ages and occupations. Mr. F was included in the sample. He was
selected by random chance from the list of participants.
Please rank the following statements in terms of which is most likely to be true of
Mr. F. (1=more likely to be true, 6=least likely)
1. ____
2. ____
3. ____
4. ____
5. ____
6. ____
Mr. F smokes more than 1 cigarette per day on average.
Mr. F has had one or more heart attacks.
Mr. F had a flu shot this year.
Mr. F eats red meat at least once per week.
Mr. F has had one or more heart attacks and he is over 55 years old.
Mr. F never flosses his teeth.
Choice 5 includes choice 3, yet 58% rated “5” more likely
than “3”. Everyone should rank “3” more likely than “”5”.
2. Conjunction Fallacy:
A health survey was conducted in a representative sample of adult males in
Chicago of all ages and occupations. Mr. F was included in the sample. He was
selected by random chance from the list of participants.
Please rank the following statements in terms of which is most likely to be true of
Mr. F. (1=more likely to be true, 6=least likely)
1. ____
2. ____
3. ____
4. ____
5. ____
6. ____
Mr. F smokes more than 1 cigarette per day on average.
Mr. F has had one or more heart attacks.
Mr. F had a flu shot this year.
Mr. F eats red meat at least once per week.
Mr. F has had one or more heart attacks and he is over 55 years old.
Mr. F never flosses his teeth.
Choice 5 includes choice 3, yet 58% rated “5” more likely
than “3”. Everyone should rank “3” more likely than “”5”.
For more information, see:
Tversky, A. and Kahneman, D. (1983).
Extensional versus intuitive reasoning: The conjunction
fallacy in probability judgment. Psychological Review, 90, 293-315.
3. Omission Bias:
In the state where you live, there have been several epidemics of a certain kind of
flu, which can be fatal to children under 3. The probability of each child getting the
flu is 1 in 10, but only 1 in 100 children who get the flu will die from it. This means
10 out of 10,000 children will die. A vaccine for this kind of flu has been developed
and tested. The vaccine eliminates the probability of getting the flu. The vaccine,
however, might cause side effects that are also sometimes fatal. The children who
die from the side effects of the vaccination are not necessarily the same ones who
would die from the flu.
Imagine that you are married and have one child, a one-year old. You wonder
whether you should vaccinate your child. Your child will have a 10 in 10,000
chance of dying from the flu without vaccination.
Would you vaccinate your child if the overall death rate for vaccinated children
were (check those in which you would vaccinate):
____ 0 in 10,000
____ 6 in 10,000
____ 1 in 10,000
____ 7 in 10,000
____ 2 in 10,000
____ 8 in 10,000
____ 3 in 10,000
____ 9 in 10,000
____ 4 in 10,000
____ 10 in 10,000
____ 5 in 10,000
3. Omission Bias:
Imagine that you are married and have one child, a one-year old. You wonder
whether you should vaccinate your child.
Your child will have a 10 in 10,000 chance of dying from the
flu without vaccination.
Would you vaccinate your child if the overall death rate for vaccinated children
were:
____ 0 in 10,000
____ 6 in 10,000
____ 1 in 10,000
____ 7 in 10,000
____ 2 in 10,000
____ 8 in 10,000
____ 3 in 10,000
____ 9 in 10,000
____ 4 in 10,000
____ 10 in 10,000
____ 5 in 10,000
Authurs found 57% stop at “8 In 10,000” or earlier thus increasing the
child’s probability of dying from flu.
3. Omission Bias:
Authors found 57% stop at “8 In 10,000” or earlier thus increasing the
child’s probability of dying from flu.
For more information, see: Ritov, I. & Baron, J. (1990).
Reluctance to vaccinate: Omission bias and ambiguity.
Journal of Behavioral Decision Making, 3, 263-277.
4. Reflection Framing Effect:
Imagine that the U.S. is preparing for outbreak of an
unusual disease, which is expected to kill 600 people. Two
alternative programs to combat the disease have been
proposed. Assume that the exact scientific estimates of the
consequences of the program are as follows:
4. Reflection Framing Effect:
Imagine that the U.S. is preparing for outbreak of an
unusual disease, which is expected to kill 600 people. Two
alternative programs to combat the disease have been
proposed. Assume that the exact scientific estimates of the
consequences of the program are as follows:
Group A is told:
If Program A is adopted, 200 people will be saved.
If Program B is adopted, there is a one-third probability
that 600 people will be saved and a two-thirds probability
that no people will be saved.
4. Reflection Framing Effect:
Imagine that the U.S. is preparing for outbreak of an
unusual disease, which is expected to kill 600 people. Two
alternative programs to combat the disease have been
proposed. Assume that the exact scientific estimates of the
consequences of the program are as follows:
Group A is told:
If Program A is adopted, 200 people will be saved. 72%
If Program B is adopted, there is a one-third probability
that 600 people will be saved and a two-thirds probability
that no people will be saved.
28%
4. Reflection Framing Effect:
Imagine that the U.S. is preparing for outbreak of an
unusual disease, which is expected to kill 600 people. Two
alternative programs to combat the disease have been
proposed. Assume that the exact scientific estimates of the
consequences of the program are as follows:
Group B is told:
If Program C is adopted, 400 people will die.
If Program D is adopted, there is a one-third probability
that nobody will die and a two-thirds probability that 600
people will die.
4. Reflection Framing Effect:
Imagine that the U.S. is preparing for outbreak of an
unusual disease, which is expected to kill 600 people. Two
alternative programs to combat the disease have been
proposed. Assume that the exact scientific estimates of the
consequences of the program are as follows:
Group B is told:
If Program C is adopted, 400 people will die.
22%
If Program D is adopted, there is a one-third probability
that nobody will die and a two-thirds probability that 600
people will die.
78%
4. Reflection Framing Effect:
Group A is told:
If Program A is adopted, 200 people will be saved. 72%
If Program B is adopted, there is a one-third probability
that 600 people will be saved and a two-thirds probability
that no people will be saved.
28%
Group B is told:
If Program C is adopted, 400 people will die.
22%
If Program D is adopted, there is a one-third probability
that nobody will die and a two-thirds probability that 600
people will die.
78%
4. Reflection Framing Effect:
Group A is told:
If Program A is adopted, 200 people will be saved. 72%
If Program B is adopted, there is a one-third probability
that 600 people will be saved and a two-thirds probability
that no people will be saved.
28%
Group B is told:
If Program C is adopted, 400 people will die.
22%
If Program D is adopted, there is a one-third probability
that nobody will die and a two-thirds probability that 600
people will die.
78%
The results are almost inverted even though Program A for Group A is logically
equal to Program C for Group B and Program B for Group A is logically equal
to Program D for Group B.
4. Reflection Framing Effect:
For more information, see: Kahneman, D. and Tversky, A. (1984).
Choices, values, and frames. American Psychologist, 39,
341-350.
5. Multiple Alternatives:
The patient is a 67-year-old farmer with chronic right hip pain. The
diagnosis is osteoarthritis. You have tried several nonsteroidal antiinflammatory agents (e.g., aspirin, naproxen, and ketoprofen) and have
stopped them because of either adverse effects or lack of efficacy. You
decide to refer him to an orthopedic consultant for consideration for hip
replacement surgery. The patient agrees to this plan.
5. Multiple Alternatives:
The patient is a 67-year-old farmer with chronic right hip pain. The
diagnosis is osteoarthritis. You have tried several nonsteroidal antiinflammatory agents (e.g., aspirin, naproxen, and ketoprofen) and have
stopped them because of either adverse effects or lack of efficacy. You
decide to refer him to an orthopedic consultant for consideration for hip
replacement surgery. The patient agrees to this plan.
Group A:
Before sending him away, however, you check the drug formulary and
find that there is one nonsteroidal medication that this patient has not
tried (ibuprofen). What do you do?
1. Refer to orthopedics and also start ibuprofen.
2. Refer to orthopedics and do not start any new medication.
5. Multiple Alternatives:
The patient is a 67-year-old farmer with chronic right hip pain. The
diagnosis is osteoarthritis. You have tried several nonsteroidal antiinflammatory agents (e.g., aspirin, naproxen, and ketoprofen) and have
stopped them because of either adverse effects or lack of efficacy. You
decide to refer him to an orthopedic consultant for consideration for hip
replacement surgery. The patient agrees to this plan.
Group A:
Before sending him away, however, you check the drug formulary and
find that there is one nonsteroidal medication that this patient has not
tried (ibuprofen). What do you do?
1. Refer to orthopedics and also start ibuprofen.
2. Refer to orthopedics and do not start any new medication.
53%
5. Multiple Alternatives:
The patient is a 67-year-old farmer with chronic right hip pain. The
diagnosis is osteoarthritis. You have tried several nonsteroidal antiinflammatory agents (e.g., aspirin, naproxen, and ketoprofen) and have
stopped them because of either adverse effects or lack of efficacy. You
decide to refer him to an orthopedic consultant for consideration for hip
replacement surgery. The patient agrees to this plan.
Group B:
Before sending him away, however, you check the drug formulary and
find that there is one nonsteroidal medication that this patient has not
tried (ibuprofen). What do you do?
1. Refer to orthopedics and also start ibuprofen.
2. Refer to orthopedics and also start piroxicam.
3. Refer to orthopedics and do not start any new medication.
72%
5. Multiple Alternatives:
The patient is a 67-year-old farmer with chronic right hip pain. The
diagnosis is osteoarthritis. You have tried several nonsteroidal antiinflammatory agents (e.g., aspirin, naproxen, and ketoprofen) and have
stopped them because of either adverse effects or lack of efficacy. You
decide to refer him to an orthopedic consultant for consideration for hip
replacement surgery. The patient agrees to this plan.
Group B:
Before sending him away, however, you check the drug formulary and
find that there is one nonsteroidal medication that this patient has not
tried (ibuprofen). What do you do?
1. Refer to orthopedics and also start ibuprofen.
2. Refer to orthopedics and also start piroxicam.
3. Refer to orthopedics and do not start any new medication.
72%
But option 2 in for Group A is the same as option 3 Group B, thus we
conclude that discovery of a new drug may lead to worse patient care.
5. Multiple Alternatives:
For more information, see:
Redelmeier, D.A. & Shafir, E. (1995). Medical decision making
in situations that offer multiple alternatives. JAMA, 273(4),
302-305
6. Attraction effect:
Imagine that one of your patients suffers from migraine headaches that last about 3 hours
and involve intense pain, nausea, dizziness, and hyper-sensitivity to bright lights and loud
noises. The patient usually needs to lie quietly in a dark room until the headache passes.
Out of every 365 days (1 year), this patient has a migraine headache on about 100 of those
days (8.3 per month). Of course, on a day when the patient has a headache, she doesn't
spend the entire day in pain, but only about 3 hours of that day.
You are considering three medications that you could prescribe for this patient. All three
medications have only negligible side effects, and any side effects are the same for the three.
Each medication comes in the form of pills that must be taken once per day.
The medications differ in effectiveness and cost. The patient has a low income and must
pay the cost because her insurance plan does not cover any of these medications. And of
course the patient is also the one who appreciates the effectiveness.
6. Attraction effect:
Imagine that one of your patients suffers from migraine headaches that last about 3 hours
and involve intense pain, nausea, dizziness, and hyper-sensitivity to bright lights and loud
noises. The patient usually needs to lie quietly in a dark room until the headache passes.
Out of every 365 days (1 year), this patient has a migraine headache on about 100 of those
days (8.3 per month). Of course, on a day when the patient has a headache, she doesn't
spend the entire day in pain, but only about 3 hours of that day.
You are considering three medications that you could prescribe for this patient. All three
medications have only negligible side effects, and any side effects are the same for the three.
Each medication comes in the form of pills that must be taken once per day.
The medications differ in effectiveness and cost. The patient has a low income and must
pay the cost because her insurance plan does not cover any of these medications. And of
course the patient is also the one who appreciates the effectiveness.
Group A: Three options
Drug A: reduces the number of headaches from 100 days with a headache per
year to 30 days with a headache per year. It costs $350 per year.
Drug B: reduces the number of headaches from 100 days with a headache per
year to 50 days with a headache per year. It costs $100 per year.
Drug C: reduces the number of headaches from 100 days with a headache per
year to 60 days with a headache per year. It costs $100 per year.
6. Attraction effect:
Imagine that one of your patients suffers from migraine headaches that last about 3 hours
and involve intense pain, nausea, dizziness, and hyper-sensitivity to bright lights and loud
noises. The patient usually needs to lie quietly in a dark room until the headache passes.
Out of every 365 days (1 year), this patient has a migraine headache on about 100 of those
days (8.3 per month). Of course, on a day when the patient has a headache, she doesn't
spend the entire day in pain, but only about 3 hours of that day.
You are considering three medications that you could prescribe for this patient. All three
medications have only negligible side effects, and any side effects are the same for the three.
Each medication comes in the form of pills that must be taken once per day.
The medications differ in effectiveness and cost. The patient has a low income and must
pay the cost because her insurance plan does not cover any of these medications. And of
course the patient is also the one who appreciates the effectiveness.
Group A: Three options
Drug A: reduces the number of headaches from 100 days with a headache per
year to 30 days with a headache per year. It costs $350 per year.
9%
Drug B: reduces the number of headaches from 100 days with a headache per
year to 50 days with a headache per year. It costs $100 per year.
81%
Drug C: reduces the number of headaches from 100 days with a headache per
year to 60 days with a headache per year. It costs $100 per year.
6. Attraction effect:
Imagine that one of your patients suffers from migraine headaches that last about 3 hours
and involve intense pain, nausea, dizziness, and hyper-sensitivity to bright lights and loud
noises. The patient usually needs to lie quietly in a dark room until the headache passes.
Out of every 365 days (1 year), this patient has a migraine headache on about 100 of those
days (8.3 per month). Of course, on a day when the patient has a headache, she doesn't
spend the entire day in pain, but only about 3 hours of that day.
You are considering three medications that you could prescribe for this patient. All three
medications have only negligible side effects, and any side effects are the same for the three.
Each medication comes in the form of pills that must be taken once per day.
The medications differ in effectiveness and cost. The patient has a low income and must
pay the cost because her insurance plan does not cover any of these medications. And of
course the patient is also the one who appreciates the effectiveness.
Group B: Two options
Drug A: reduces the number of headaches from 100 days with a headache per
year to 30 days with a headache per year. It costs $350 per year.
Drug B: reduces the number of headaches from 100 days with a headache per
year to 50 days with a headache per year. It costs $100 per year.
6. Attraction effect:
Imagine that one of your patients suffers from migraine headaches that last about 3 hours
and involve intense pain, nausea, dizziness, and hyper-sensitivity to bright lights and loud
noises. The patient usually needs to lie quietly in a dark room until the headache passes.
Out of every 365 days (1 year), this patient has a migraine headache on about 100 of those
days (8.3 per month). Of course, on a day when the patient has a headache, she doesn't
spend the entire day in pain, but only about 3 hours of that day.
You are considering three medications that you could prescribe for this patient. All three
medications have only negligible side effects, and any side effects are the same for the three.
Each medication comes in the form of pills that must be taken once per day.
The medications differ in effectiveness and cost. The patient has a low income and must
pay the cost because her insurance plan does not cover any of these medications. And of
course the patient is also the one who appreciates the effectiveness.
Group B: Two options
Drug A: reduces the number of headaches from 100 days with a headache per
year to 30 days with a headache per year. It costs $350 per year.
36%
Drug B: reduces the number of headaches from 100 days with a headache per
year to 50 days with a headache per year. It costs $100 per year.
64%
6. Attraction effect:
Group A: Three options
Drug A: reduces the number of headaches from 100 days with a headache per
year to 30 days with a headache per year. It costs $350 per year.
9%
Drug B: reduces the number of headaches from 100 days with a headache per
year to 50 days with a headache per year. It costs $100 per year.
81%
Drug C: reduces the number of headaches from 100 days with a headache per
year to 60 days with a headache per year. It costs $100 per year.
Group B: Two options
0%
Drug A: reduces the number of headaches from 100 days with a headache per
year to 30 days with a headache per year. It costs $350 per year.
36%
Drug B: reduces the number of headaches from 100 days with a headache per
year to 50 days with a headache per year. It costs $100 per year.
64%
6. Attraction effect:
Group A: Three options
Drug A: reduces the number of headaches from 100 days with a headache per
year to 30 days with a headache per year. It costs $350 per year.
9%
Drug B: reduces the number of headaches from 100 days with a headache per
year to 50 days with a headache per year. It costs $100 per year.
81%
Drug C: reduces the number of headaches from 100 days with a headache per
year to 60 days with a headache per year. It costs $100 per year.
Group B: Two options
0%
Drug A: reduces the number of headaches from 100 days with a headache per
year to 30 days with a headache per year. It costs $350 per year.
36%
Drug B: reduces the number of headaches from 100 days with a headache per
year to 50 days with a headache per year. It costs $100 per year.
64%
But the information about Drugs A and B in the three option version is
the same as the information about Drugs A and B in the two option
version. The addition of the Drug C, although chosen by no one, has
increased the selection of Drug B.
6. Attraction effect:
For more information, see: Huber, J., Payne, J.W. & Puto, C. (1982). Adding
asymmetrically dominated alternatives: Violations of regularity and the
similarity hypothesis. Journal of Consumer Research, 9(1), 90-98;
and
Chapman, G.B. & Malik, M.M. (1995). The attraction effect in prescribing
decisions and consumer choice. Medical Decision Making, 15, 414.
7. Outcome bias:
A 55-year-old man had a heart condition. He had to stop working because of chest pain.
He enjoyed his work and did not want to stop. His pain also interfered with other things,
such as travel and recreation. A type of bypass operation would relieve his pain and increase
his life expectancy from age 65 to age 70. However, 8% of the people who have this
operation die from the operation itself. His physician decided to go ahead with the
operation.
1. The physician who made the decision first consulted the patient. The patient could not decide and
asked the physician's advice. The physician knew that the patient would accept this advice. Hence, it is
the physician who makes the decision on the patient's behalf.
2. The physician who made the decision is not the one who carried out the procedure.
3. The physician who made the decision had no more relevant information than you are given, and
there is no more relevant information that can be discovered.
Evaluate the physician's decision to go ahead with the operation (circle one):
3
2
1
0
-1
-2
-3
=clearly correct, and the opposite decision would be inexcusable
=correct, all things considered
=correct, but the opposite would be reasonable too
=decision and its opposite are equally good
=incorrect, but not unreasonable
=incorrect, all things considered
=incorrect and inexcusable
7. Outcome bias:
Group A:
A 55-year-old man had a heart condition. He had to stop working because of chest pain.
He enjoyed his work and did not want to stop. His pain also interfered with other things,
such as travel and recreation. A type of bypass operation would relieve his pain and increase
his life expectancy from age 65 to age 70. However, 8% of the people who have this
operation die from the operation itself. His physician decided to go ahead with the
operation. The operation succeeded.
7. Outcome bias:
Group A:
A 55-year-old man had a heart condition. He had to stop working because of chest pain.
He enjoyed his work and did not want to stop. His pain also interfered with other things,
such as travel and recreation. A type of bypass operation would relieve his pain and increase
his life expectancy from age 65 to age 70. However, 8% of the people who have this
operation die from the operation itself. His physician decided to go ahead with the
operation. The operation succeeded.
The mean score was .85
7. Outcome bias:
A 55-year-old man had a heart condition. He had to stop working because of chest pain.
He enjoyed his work and did not want to stop. His pain also interfered with other things,
such as travel and recreation. A type of bypass operation would relieve his pain and increase
his life expectancy from age 65 to age 70. However, 8% of the people who have this
operation die from the operation itself. His physician decided to go ahead with the
operation. The operation succeeded. or The operation failed and the man died.
The mean score was .85
Group B:
A 55-year-old man had a heart condition. He had to stop working because of chest pain.
He enjoyed his work and did not want to stop. His pain also interfered with other things,
such as travel and recreation. A type of bypass operation would relieve his pain and increase
his life expectancy from age 65 to age 70. However, 8% of the people who have this
operation die from the operation itself. His physician decided to go ahead with the
operation. The operation failed and the man died.
7. Outcome bias:
Group A:
A 55-year-old man had a heart condition. He had to stop working because of chest pain.
He enjoyed his work and did not want to stop. His pain also interfered with other things,
such as travel and recreation. A type of bypass operation would relieve his pain and increase
his life expectancy from age 65 to age 70. However, 8% of the people who have this
operation die from the operation itself. His physician decided to go ahead with the
operation. The operation succeeded.
The mean score was .85
Group B:
A 55-year-old man had a heart condition. He had to stop working because of chest pain.
He enjoyed his work and did not want to stop. His pain also interfered with other things,
such as travel and recreation. A type of bypass operation would relieve his pain and increase
his life expectancy from age 65 to age 70. However, 8% of the people who have this
operation die from the operation itself. His physician decided to go ahead with the
operation. The operation failed and the man died.
The mean score was -.05.
7. Outcome bias:
A 55-year-old man had a heart condition. He had to stop working because of chest pain.
He enjoyed his work and did not want to stop. His pain also interfered with other things,
such as travel and recreation. A type of bypass operation would relieve his pain and increase
his life expectancy from age 65 to age 70. However, 8% of the people who have this
operation die from the operation itself. His physician decided to go ahead with the
operation. The operation succeeded. or The operation failed and the man died.
The operation succeeded : The mean score was .85
The operation failed and the man died: The mean score was -.05.
7. Outcome bias:
A 55-year-old man had a heart condition. He had to stop working because of chest pain.
He enjoyed his work and did not want to stop. His pain also interfered with other things,
such as travel and recreation. A type of bypass operation would relieve his pain and increase
his life expectancy from age 65 to age 70. However, 8% of the people who have this
operation die from the operation itself. His physician decided to go ahead with the
operation. The operation succeeded. or The operation failed and the man died.
The operation succeeded : The mean score was .85
The operation failed and the man died: The mean score was -.05.
Thus the advice, that had to given before the
operation, was declared to be correct or incorrect
based upon the result.
7. Outcome bias:
For more information see: Baron, J. and Hershey, J.C. (1988). Outcome bias in decision
evaluation. JPSP, 54, 569-579.