Thinking: Reasoning and Decisions.

Question 1

Define reasoning.

Answer 1

Reasoning has been defined as the process of drawing conclusions and the cognitive processes by which people start with information and come to conclusions to go beyond that information.

Question 2

Cognitive psychologists often make a distinction between two different kinds of reasoning.

Answer 2

Much like philosophers, cognitive psychologists make a distinction between deductive and inductive reasoning.

Question 3

What is deductive reasoning?

Answer 3

Deductive reasoning involves sequences of statements called syllogisms.

Question 4

What is inductive reasoning?

Answer 4

Inductive reasoning is reaching conclusions from evidence. In inductive reasoning, conclusions are suggested, with varying degrees of certainty, but do not definitely follow from premises.

Question 5

What is a syllogism? Give an example.

Answer 5

The basic form of deductive reasoning as introduced by Aristotle is called the syllogism. A syllogism includes two statements, called premises, followed by a third statement, called the conclusion.

Syllogism 1:
Premise 1: All birds are animals.
Premise 2: All animals eat food.
Conclusion: Therefore, all birds eat food.

Question 6

Syllogism 1:
Premise 1: All birds are animals.
Premise 2: All animals eat food.
Conclusion: Therefore, all birds eat food.

If you were to evaluate this syllogism, what two factors would you look at?

Answer 6

Its validity and its truth.

Question 7

What is validity in syllogisms?

Answer 7

A syllogism is valid when its conclusion follows logically from its two premises.

Question 8

What is truth in syllogisms?

Answer 8

The truth of a syllogism depends on the truth of its premises. If the premises are false, the conclusion may also be false despite being logically valid.

Question 9

Syllogism 3
All of the students are tired.
Some tired people are irritable.
Some of the students are irritable.

Evaluate the syllogism.

Answer 9

Statistically some students could be irritable, yes - because they are tired people. But they could also be not irritable because some tired people are not irritable. We just don’t know. Therefore the conclusion: “some of the students are irritable” is invalid.

Question 10

The book teaches two different types of syllogisms. Which?

Answer 10

1. Categorical syllogisms.

2. Conditional syllogisms.

Question 11

What is a categorical syllogism?

Answer 11

A categorical syllogism is a syllogism in which the premises and the conclusion describe the relation between two categories by using statements that begin with all, no, or some.

Question 12

What is a conditional syllogism?

Answer 12

Conditional syllogisms have two premises and a conclusion, just like categorical ones, but the first premise has the form “ if … then… “.

Question 13

There are four different conditional syllogisms. Which?

Answer 13

1. Affirming the antecedent.
2. Denying the consequent.
3. Affirming the consequent
4. Denying the antecedent.

Question 14

What is the antecedent?

Answer 14

The antecedent is the “if” term of the syllogism. E.g. “If i study”.

Question 15

What is the consequent?

Answer 15

The consequent is the “then” term of the syllogism. E.g. “then I’ll get a good grade”.

Question 16

If I study, then I’ll get a good grade.
I got a good grade.
Therefore, I studied.

Name the syllogism and its validity. Explain.

Answer 16

This is affirming the consequent because q is affirmed in the second premise (I got a good grade). The concluson of this syllogism (I studied) is invalid, because if if you didn’t study, it is still possible that you could have receieved a good grade. Perhaps the exam was easy, or maybe you knew the material because it was about your job experience.

Question 17

If I study, then I’ll get a good grade.
I didn’t get a good grade.
Therefore, I didn’t study.

Name the syllogism and its validity. Explain.

Answer 17

This is denying the consequent because the consequent (I’ll get a good grade) is negated in the second premise (I didn’t get a good grade). The conclusion of this syllogism (I didn’t study) is valid.

Question 18

If I study, then I’ll get a good grade.
I didn’t study.
Therefore, I didn’t get a good grade.

Name the syllogism and its validity. Explain.

Answer 18

This is denying the antecedent because p is negated in the second premise (I didn’t study). The conclusion of this syllogism (I didn’t get a good grade) is not valid. It is possible to get a good grade even though you don’t study.

Question 19

If I study, then I’ll get a good grade.
I studied.
Therefore, I’ll get a good grade.

Name the syllogism and its validity. Explain.

Answer 19

This is affirming the antecedent because the antecedent, p (if I study), is affirmed in the second premise (I studied). The conclusion of this syllogism (I got a good grade) is valid.

Question 20

Only about 40% of people correctly identify that the affirming the consequent syllogism is logically invalid. Use an example of this syllogism that clearly shows its invalidity.

Answer 20

If it’s a robin, then it’s a bird.
It’s a bird.
Therefore, It’s a robin.

Question 21

Only about 40% of people correctly identify that the denying the antecedent syllogism is logically invalid. Use an example of this syllogism that clearly shows its invalidity.

Answer 21

If it’s a robin, then it’s a bird.
It’s not a robin.
Therefore, it’s not a bird.

Question 22

What percentage of people correctly identify that affirming the antecedent syllogisms are valid?

Answer 22

About 97%.

Question 23

What percentage of people correctly identify that denying the consequent syllogisms are valid?

Answer 23

About 60%.

Question 24

Does abstraction, like using p and q, make it easier or more difficult to judge the validity of syllogisms?

Answer 24

Research shows that people are often better at judging the validity of syllogisms when real-world examples are substituted for abstract symbols.

Question 25

A very common problem used in the research on conditional reasoning has been …

Answer 25

the Wason Four-Card Problem.

Question 26

What is the Wason Four-Card Problem?

Answer 26

Four cards are shown. Each card has a letter on one side and a number on the other side. Your task is to indicate which cards you would need to turn over to test the following rule: If there is a vowel on one side, then there is an even number on the other side.

E - K - 4 - 7

Question 27

How many percent of people correctly solved the Wason Four-Card Problem in the original study?

Answer 27

Only 7%.

Question 28

Four cards are shown. Each card has a letter on one side and a number on the other side. Your task is to indicate which cards you would need to turn over to test the following rule: If there is a vowel on one side, then there is an even number on the other side.

E - K - 4 - 7

Answer 28

You need to turn over E and 7.
If you turn over the E and there is an odd number, the rule is falsified. If there is an even number however, the rule is not yet confirmed.
You also need to turn over 7.
If you turn over 7 and there is a vowel, the rule is falsified.

Question 29

Four cards are shown. Each card has a letter on one side and a number on the other side. Your task is to indicate which cards you would need to turn over to test the following rule: If there is a vowel on one side, then there is an even number on the other side.

E - K - 4 - 7

You turn over E and the result is Even. How does this affect the rule?

Answer 29

It confirms it.

Question 30

Four cards are shown. Each card has a letter on one side and a number on the other side. Your task is to indicate which cards you would need to turn over to test the following rule: If there is a vowel on one side, then there is an even number on the other side.

E - K - 4 - 7

You turn over E and the result is Odd. How does this affect the rule?

Answer 30

It falsifies it.

Question 31

Four cards are shown. Each card has a letter on one side and a number on the other side. Your task is to indicate which cards you would need to turn over to test the following rule: If there is a vowel on one side, then there is an even number on the other side.

E - K - 4 - 7

You turn over K and the result is Even. How does this affect the rule?

Answer 31

It is irrelevant to the rule.

Question 32

Four cards are shown. Each card has a letter on one side and a number on the other side. Your task is to indicate which cards you would need to turn over to test the following rule: If there is a vowel on one side, then there is an even number on the other side.

E - K - 4 - 7

You turn over K and the result is Odd. How does this affect the rule?

Answer 32

It is irrelevant to.

Question 33

Four cards are shown. Each card has a letter on one side and a number on the other side. Your task is to indicate which cards you would need to turn over to test the following rule: If there is a vowel on one side, then there is an even number on the other side.

E - K - 4 - 7

You turn over 4 and the result is Vowel. How does this affect the rule?

Answer 33

It confirms the rule.

Question 34

Four cards are shown. Each card has a letter on one side and a number on the other side. Your task is to indicate which cards you would need to turn over to test the following rule: If there is a vowel on one side, then there is an even number on the other side.

E - K - 4 - 7

You turn over 4 and the result is Consonant. How does this affect the rule?

Answer 34

It is irrelevant to the rule

Question 35

Four cards are shown. Each card has a letter on one side and a number on the other side. Your task is to indicate which cards you would need to turn over to test the following rule: If there is a vowel on one side, then there is an even number on the other side.

E - K - 4 - 7

You turn over 7 and the result is Vowel. How does this affect the rule?

Answer 35

It falsifies the rule

Question 36

Four cards are shown. Each card has a letter on one side and a number on the other side. Your task is to indicate which cards you would need to turn over to test the following rule: If there is a vowel on one side, then there is an even number on the other side.

E - K - 4 - 7

You turn over 7 and the result is Consonant. How does this affect the rule?

Answer 36

It is irrelevant to the rule.

Question 37

Four cards are shown. Each card has an age on one side and the name of a beverage on the other side. Imagine you are a police officer who is applying the rule: “If a person is drinking beer, then he or she must be over 19 years old”. Which of the cards must be turned over to determine whether the rule is being followed?

Beer - Soda - 16 Years old - 24 Years old.

Answer 37

The correct answer is that you need to turn over both the “beer” and the “16 years old”.

Question 38

Four cards are shown. Each card has an age on one side and the name of a beverage on the other side. Imagine you are a police officer who is applying the rule: “If a person is drinking beer, then he or she must be over 19 years old”. Which of the cards must be turned over to determine whether the rule is being followed?

Beer - Soda - 16 Years old - 24 Years old.

How many percent got this right in Griggs and Cox’ study?

Answer 38

About 73% percent. In contrast, none of their participants answered the abstract task correctly.

Question 39

Patricia Cheng and Keith Holyoak (1985) took the Wason task a step further by proposing the concept of pragmatic rasoning schemas. What are they?

Answer 39

A pragmatic reasoning schema is a way of thinking about cause and effect in the world that is learned as a part of experiencing everyday life.

Question 40

A pragmatic reasoning schema is a way of thinking about cause and effect in the world that is learned as a part of experiencing everyday life. How does this affect performance on the Wason task?

Answer 40

According to Patricia Cheng and Keith Holyoak’s 1985 hypothesis, the performance on the Wason task depends on our permission schema. A permission schema is a schema that states that if a person satisfies condition A (such as being the legal age for drinking), then he or she gets to carry out action B (being served alchohol). The permission schema is something most of the participants in the Griggs and Cox experiment had learned, so they were able to apply that schema to the card task.

Question 41

You are an immigration officer at the International Airport in Manila, capital of the Philippines. Among the documents you have to check is a sheet called Form H. One side of this firm indicates whether the passenger is entering the country or in transit, and the other side of the firm lists names of tropical diseases. You have to make sure that if the form says “Entering” on one side, the other side includes cholera among the list of diseases. Which of the following forms would you have to turn over to check? Indicate only those that you need to check to be sure.

Entering - Transient - Cholera, Typhoid, Hepatitis - Typhoid, Hepatitis

Answer 41

You need to check the “Entering” and the “Typhoid, Hepatitis”.

Question 42

You are an immigration officer at the International Airport in Manila, capital of the Philippines. Among the documents you have to check is a sheet called Form H. One side of this firm indicates whether the passenger is entering the country or in transit, and the other side of the firm lists names of tropical diseases. You have to make sure that if the form says “Entering” on one side, the other side includes cholera among the list of diseases. Which of the following forms would you have to turn over to check? Indicate only those that you need to check to be sure.

Entering - Transient - Cholera, Typhoid, Hepatitis - Typhoid, Hepatitis

Using the hypothesis of permission schemas, how easy do you think this task would be?

Answer 42

It is taken from Cheng and Holyoak’s 1985 experiment, and is meant to avoid using the permission schema. It is thought that the participants would think of this task as checking whether the correct diseases are listed on the form. The prediction, that was met in their results, is that this would be more difficult than a similar text that calls upon the permission schema.

Question 43

You are an immigration officer at the International Airport in Manila, capital of the Philippines. Among the documents you have to check is a sheet called Form H. One side of this firm indicates whether the passenger is entering the country or in transit, and the other side of the form lists inoculations the passengers have received in the past 6 months. You have to make sure that if the form says “Entering” on one side, the other side includes cholera among the list of diseases. This is to ensure that entering passengers are protected against the disease. Which of the following forms would you have to turn over to check? Indicate only those that you need to check to be sure.

Entering - Transient - Cholera, Typhoid, Hepatitis - Typhoid, Hepatitis

Using the hypothesis of permission schemas, how easy do you think this task would be?

Answer 43

This is taken from Cheng and Holyoak’s 1985 experiment, and is the text from the permission schema group. They hoped that they would call upon this schema by causing them to take upon themselves the role of the immigration officer, and that this immigration officer was checking to see if they had what was necessary to be granted permission to enter the country. Cheng and Holyoak achieved the results they predicted: more people came up with the correct answer when they were thought to use the permission schema.

Question 44

Are there other hypotheses than permission schema to the differences in performance that was found in Cheng and Holyoak’s , and Griggs and Cox’ experiments?

Answer 44

Yes. One proposed alternative to a permission schema is that performance on the Wason task is governed by a built-in cognitive program for detecting cheating.

Question 45

How can the differences in performance that was found in Cheng and Holyoak’s , and Griggs and Cox’ experiments be explained as “cognitive programs for detecting cheating?”

Answer 45

The evolutionary approach proposes that the Wason problem can be understood in terms of cheating. Thus, people do well in the cholera task because they can detect someone who cheats by entering the country without a cholera shot. Compared to the other researchers, these researchers find it a better idea to propose a schema that has a reason to be there.

Question 46

The evolutionary approach proposes that the Wason problem can be understood in terms of cheating. Thus, people do well in the cholera task because they can detect someone who cheats by entering the country without a cholera shot. Compared to the other researchers, these researchers find it a better idea to propose a schema that has a reason to be there. What evidence did they produce to back this?

Answer 46

Cosmides and Tooby (1992) devised a number of four-card scenarios involving unfamiliar situations. Remember that one idea behind the permission schema is that people perform well because they are familiar with the various rules. Despite the “unfamiliar” situations, the scores remained high.

Question 47

A number of factors can contribute to the strength of an inductive argument. Among them are ….

Answer 47

1. Representativeness of observations.
2. Number of observations.
3. Quality of the evidence.

Question 48

A number of factors can contribute to the strength of an inductive argument. Among them are representativeness of observations. Explain.

Answer 48

How well do the observations about a particular category represent all of the members of that category? Clearly, the crows example suffers from a lack of representativeness because it does not consider crows from other parts of the country. If there are rare blue crows in California, then the conclusion is not true.

Question 49

A number of factors can contribute to the strength of an inductive argument. Among them are number of observations. Explain

Answer 49

The argument about the crows is made stronger by adding the Washington, DC, observations to the Pittsburgh observations. Adding more observations would strengthen it further. The conclusion about the sun rising in Tuscon is extremely strong because it is supported by a very large number of observations.

Question 50

A number of factors can contribute to the strength of an inductive argument. Among them are quality of evidence. Explain.

Answer 50

Stronger evidence results in stronger conclusions. For example, although the conclusion “The sun will rise in Tuscon” is extremely strong because of the number of observations, it becomes even stronger when we consider scientific descriptions of how the earth rotates on its axis and revolves around the sun. Thus, adding the observations “Scientific measurements of the rotation of the earth indicate that every time the earth rotates the sun will appear to rise” strengthens the conclusion even further.

Question 51

There are two examples of inductive reasoning it’d be wise to remember. Which?

Answer 51

Observation: All the crows I’ve seen in Pittsburgh are black. When I visited my brother in Washington, DC, the crows I saw there were black too.
Conclusion: I think it is a pretty good bet that all crows are black.

Observation: Here in Tuscon, the sun has risen every morning.
Conclusion: The sun is going to rise in Tuscon tomorrow.

Question 52

Do people actually use inductive reasoning in their daily life?

Answer 52

Yes, and no. Inductive reasoning is reasoning from observation, from experience. That is something we do, but we do not necessarily follow a rigorous logic when creating conclusions. We use heuristics.

Question 53

What are heuristics?

Answer 53

Heuristics are “rules of thumb”, shortcuts in reasoning, that are likely to provide the correct answer to a problem, but are not foolproof.

Question 54

Two different categories of heuristics are relevant to reasoning. Which?

Answer 54

1. Availability heuristic

2. Representative heuristic.

Question 55

Short: what is the availability heuristic?

Answer 55

The availability heuristic states that events that are more easily remembered are judged as more probably than events that are easily remembered.

Question 56

Short: what is the representative heuristic?

Answer 56

The representativeness heuristic states that the probability that A is a member of class B can be determined by how well the properties of A resembles the properties we usually associate with class B.

Question 57

Which are more prevalent in English, words that begin with the letter r or words in which r is the third letter? Explain what happens when people are asked this question, and why this happens.

Answer 57

Three times more words have r in the third position than in the first. However, 70% of participants respond that more words begin with r. (Tversky & Kahneman, 1973). According to the hypothesis of the availability heuristic, people really have no idea in this case - which would predict a 50/50 divide. This does not happen because it is much more easy to remember words that begin with an r than words that have r in the third position.

Question 58

We randomly pick one male from the population of the United States. That male, Robert, wears glasses, speaks quietly, and reads a lot. Is it more likely that Robert is a librarian or a farmer?

Answer 58

When Amos Tversky and Daniel Kahneman (1974) presented this question in an experiment, more people guessed that Robert was a librarian. This is because Robert has the characteristics of a typical librarian. However, they were ignoring another important source of information - the base rates of farmers and librarians in the population. This demonstrates a case where the representativeness heuristic causes us to arrive at the wrong conclusion.

Question 59

Linda is 31 years old, single, outspoken, and very bright. She majored in philosophy. As a student, she was deeply concerned with issues of discrimination and social justice, and also participated in antinuclear demonstrations. Which of the following is more probable?

1. Linda is a bank teller.
2. Linda is a bank teller and is active in the feminist movement.

Answer 59

The correct answer to this problem is that statement 1 has the greater probability of being true, but when Tversky and Kahneman (1983) posed this problem to their participants, 85 percent picked statement 2. This also demonstrates the representativeness heuristic.

Question 60

A certain town is served by two hospitals. In the larger hospital about 45 babies are born each day, and in the smaller hospital about 15 babies are born each day. As you know, about 50 percent of all babies are boys. However, the exact percentage varies from day to day. Sometimes it may be higher than 50 percent, sometimes lower.
From a period of 1 year, each hospital recorded the days on which more than 60 percent of the babies born were boys. Which hospital do you think recorded more such days?

1. The larger hospital?
2. The small hospital?
3. About the same.

Answer 60

When participants were asked this question in an experiment (Tversky & Kahneman, 1974), 22 percent picked the larger hospital, 22 percent picked the small hospital, and 56 percent stated that there would be no difference. The correct answer is that there would be more days with over 60 percent male birth in the small hospital. This seems to be a feature of the representativeness heuristic - that smaller samples are representative - which they are not.

Question 61

What is confirmation bias?

Answer 61

Confirmation bias is our tendency to selectively look for information that conforms to our hypothesis and to over-look information that argues against it.

Question 62

How can you demonstrate confirmation bias?

Answer 62

Wason (1960) demonstrated it by presenting his participants with the task of discovering his rule for the organisation of three numbers. They were to attempt to guess his rule when they felt confident that they knew it, yet most people guessed too early because they did not try to falsify their own hypotheses. Wason gave them the numbers 2, 4, 6. The rule was “three numbers in increasing order of magnitude”.

Question 63

How do people react to evidence when they already have an opinion on the matter?

Answer 63

Charles Lord and coworkers (1979) provided a participant group that was in favor of capital punishment, and one that was against, with research studies on the deterrent effect it had on murder (some were negative, others positive). They rated the articles that confirmed their own view as convincing, and the articles that did not confirm their view as unconvincing.

Question 64

Which factors that influence decision making has been researched?

Answer 64

1. Utility.
2. Emotions.
3. How the problems are framed.
4. The need to justify the decision.

Question 65

How is utility a part of decision making?

Answer 65

Much of the early theorizing on decision making was influenced by expected utility theory. This theory is based on the assumption that people are basically rational, so if they have all of the relevant information, they will make a decision that results in the maximum expected utility.

Question 66

In expected utility theory, define utility.

Answer 66

Utility refers to outcomes that achieve a person’s goals.

Question 67

How well does expected utility theory explain people’s decision making? Mention one experiment.

Answer 67

Not too well. Most research into these topics indicate that people are not very good everyday statisticians. Denes-Raj and Epstein (1994) gave participants a choice between randomly picking one jelly bean from (a) a bowl with 1 red bean and 9 white beans, or (b) a bowl with 7 red beans and 93 white beans. Participants received money if they picked a red bean. Many participants chose the larger bowl.

Question 68

How do emotions affect decision?

Answer 68

Research has shown that people often show risk aversion because they are trying to avoid negative emotions, but research has also shown that people overestimate how negatively they will feel about losing. A person’s mood can possible influence economic decisions.

Question 69

What research has been done on the prediction of negative emotions and risk aversion?

Answer 69

Deborah Kermer and cowrokers (2006) studied this effect by doing an experiment that compared people’s expected emotion with their actual emotions. They gave participants $5 and told them that based on a coin flip they would either win an additional $5 or lose $3. Participants rated how happy or sad they’d feel if they won or lost money. After the coin toss, they carried out a filler task for 10 minutes and then rated their happiness. Participants overestimated how negative they’d feel.

Question 70

Can the way problems are worded influence decision making?

Answer 70

Yes, of course. Paul Slovic and coworkers (2000) showed forensic psychologists and psychiatrists a case history of a mental patient, and asked them to judge whether the patient should be discharged or not. “20 out of every 100 patients similar to Mr. Jones are estimated to commit an act of violence” caused 41% of the participants to refuse to discharge the patient, whereas “patients similar to Mr. Jones are estimated to have a 20 percent chance of committing an act of violence”, caused only 21% to refuse discharge.

Question 71

Paul Slovic and coworkers (2000) showed forensic psychologists and psychiatrists a case history of a mental patient, and asked them to judge whether the patient should be discharged or not. “20 out of every 100 patients similar to Mr. Jones are estimated to commit an act of violence” caused 41% of the participants to refuse to discharge the patient, whereas “patients similar to Mr. Jones are estimated to have a 20 percent chance of committing an act of violence”, caused only 21% to refuse discharge.

Why do you think this happened?

Answer 71

One possibility is that the first statement conjures up images of 20 people being beaten up. One is one too many! The other statement causes you to think only of this case, and how the chance that Mr. Jones will be violent is quite low.

Question 72

Imagine that the United States is preparing for an outbreak of an unusual disease that 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:

• If Program A is adopted, 200 people will be saved.
• If Program B is adopted, there is a 1/3 probability that 600 people will be saved, and a 2/3 probability that no people will be saved.

Which of the two programs would you favor?
Now consider the following additional proposals for combating the same disease:

• If Program C is adopted, 400 people will die.
• If Program D is adopted, there is a 1/3 probability that nobody will die, and a 2/3 probability that 600 people will die.

Which of these two programs would you pick?

Answer 72

They are all equal, but Tversky and Kahneman (1981) discovered that when asked this most participants chose program A over program B (72%), and program D over Program C (78%). Tversky and Kahneman concluded that, in general, when a choice is framed in terms of gains (as in the first problem, which is stated in terms of saving lives), people use a risk aversion strategy, and when a choice is framed in terms of losses (as in the second problem, which is stated in terms of losing lives), people use a risk-taking strategy. These results illustrate the framing effect - decisions are influenced by how the choices are stated, or framed.

Question 73

How can our need to justify our choices influence them?

Answer 73

Tversky and Eldar Shafir (1992) conducted an experiment in which they presented participants with a choice to buy a vacation package or not. One group was given plausible reasons to justify them deserving the vacation, while the other were not given that. This seemed to have an effect on the choice to buy a vacation or not.

Question 74

Imagine that you have just taken a tough qualifying examination. It is the end of the semester, you feel tired and run-down, and you find out that you passed the exam. You now have the opportunity to buy a very attractive 5-day Christmas vacation package to Hawaii at an exceptionally low price. The special offer expires tomorrow. Would you

• Buy the vacation package?
• Not buy the vacation package?
• Pay a $5 nonrefundable fee in order to retain the right to buy the vacation package at the same exceptional price the day after tomorrow?

This was presented, along with a failed exam and a delayed answer condition. What were the results?

Answer 74

The choices were similar between the failed and passed groups, but somehow different for the delayed answer condition (in which the participants were told that their exam results wouldn’t arrive yet.) Thus, 61 % percent of the participants in this group did not want to make a decision about the trip until they found out whether they had passed or failed, even though the results for the other two groups indicate that passing or failing made no difference on the actual decision about the vacation packages.

Question 75

Imagine that there is a deadly flu going around you area next winter. Your doctor says that you have a 10 percent chance of dying from this flu. A new flu vaccine has been developed and tested. If administered, the vaccine will prevent you from catching the deadly flu. However, there is one serious risk involved: the vaccine is made from a somewhat weaker type of flu virus, so there is a 5 percent risk that the vaccine could kill you. Will you take the vaccine?

Answer 75

Yes, but 52% of the participants in the study where this problem stems from (Brian Zikmund-Fisher and coworkers, 2006) would not. This result is an example of omission bias - the tendency to do nothing to avoid having to make a decision that could be interpreted as causing harm.