1. © 2010 by W. W. Norton & Co., Inc.
Judgment and Reasoning
Chapter 11
Lecture Outline

2. Chapter 12: Judgment and Reasoning
 Lecture Outline
 Judgment Heuristics
 Anchoring
 Detecting Covariation
 Assessing the Damage
 Confirmation and Disconfirmation
 Logic
 Decision Making

3. Judgment Heuristics
 Induction （歸納） is a pattern of
reasoning in which one seeks to draw
general claims from specific bits of
evidence
 Based on what you know about Allen, what is
likely to cheer him up today?
 Based on what you know about cars, what is
the best kind to buy?

4. Judgment Heuristics
 Heuristic （捷思）
 Reasonably efficient and accurate
 Gain efficiency lose accuracy
 Judgment heuristics include
 Attribute substitution
 Availability heuristic
 Representativeness heuristic

5. Judgment Heuristics
 Attribute substitution is a strategy used
when we do not have easy access to a
desired piece of information
 Instead, we base our decision on readily
available information (a proxy or index)
that we believe is correlated with the
desired information

6. Judgment Heuristics
 Ease of reading =
author intelligence

7. Judgment Heuristics
 Availability heuristic
 Specific case of attribute substitution
 Ease with which examples come to mind is
an index of frequency or likelihood
 This class is easy—I know four people who got
A’s.

8. Judgment Heuristics
 For instance, consider
 In the English language, are there more
words that start with the letter “R” or with the
letter “R” in the third position?
 Who washes the dishes more often, you or
your roommates?
 Are more deaths caused by crimes or by
diseases?

9. Judgment Heuristics
 The availability heuristic
 More words that begin with “R”
 Reality
 More words with “R” in the third position,
 But words that begin with “R” are easier to
bring to mind

10. Judgment Heuristics
 The availability
heuristic may lead us
to believe that we
always do the
housework ourselves

11. Judgment Heuristics
 The availability
heuristic may lead us
to think that more
deaths are caused by
crimes or accidents
than by disease
 In reality, far more
deaths are caused by
disease

12. Judgment Heuristics
 Availability heuristic
 Group of students asked to recall past
episodes in which they had been assertive
(Schwarz et al., 1991)
 One group gave 6 examples, and another, 12
examples
 Which group then judged themselves to be
more assertive in general?

13. Judgment Heuristics
 Those that gave 6 examples judged
themselves as more assertive
 Easier to come up with 6 examples

14. Judgment Heuristics
 The representativeness heuristic is
another example of attribute substitution
Member Prototype Category
resembles resembles

15. Judgment Heuristics
 For instance, consider
 Do you assume anything about someone if
you discover that he or she is a lawyer or an
engineer?
 If a coin toss results in “heads” six times in a
row, what are the odds of getting “tails” the
seventh time?
 If you hear an anecdote about a marathon
runner who has smoked for decades and is
perfectly healthy, does this mean that
smoking is safe?

16. Judgment Heuristics
 The representativeness heuristic
 All lawyers or all engineers are
homogeneous (a stereotype)
 We assume that each individual member of a
category has the traits we associate with the
category overall.

17. Judgment Heuristics
 The representativeness heuristic
 The seventh coin toss is more likely to be tails
(the gambler’s fallacy), but the odds are still
50-50

18. Judgment Heuristics
 The representativeness heuristic
 Smoking must be okay for your health based
on one example (anecdotal evidence or “man
who” stories)
 This is an example of reasoning from one
instance to the population.

19. Judgment Heuristics
 Representativeness heuristic
 Watched “prison guard” discussing his job (Hamill et
al., 1980)
 One variable of the study was whether the
guard was compassionate or contemptuous.
Another variable was whether the participants
were told the guard was representative of all
guards.
 What did participants later conclude about
prison guards in general?

20. Judgment Heuristics
Compassionate Contemptuous
Representative Compassionate Contemptuous
Not Representative Compassionate Contemptuous
Judgments were based on characteristics independent of whether
participants were told the guard was representative or not

21. Detecting Covariation
 Covariation
 Relationship between two variables
 Negative or positive and can vary in strength.
 Does college education lead to a higher paying
job?
 Do you feel better when you have a good
breakfast?

22. Detecting Covariation
 An illusory covariation
 A perceived pattern such that
one variable predicts another
 A study of Rorschach inkblots
found that even when fictitious
patients and fictitious
responses were randomly
paired, people believed they
had found patterns.
 Other studies have found that
clinicians believed that
homosexuals and
heterosexuals interpreted these
images differently even though
the data did not show this.

23. Detecting Covariation
 Confirmation bias
 More responsive to evidence that confirms
one’s beliefs
 Similar to overregularization by schemata
 Essentially we ignore disconfirming data

24. Detecting Covariation
 Big dogs are vicious
 Notice examples that fit this pattern more
readily (biased attention)
 Will recall examples that fit the pattern more
readily (biased memory)

25. Detecting Covariation
 Another reason that estimates of
covariation can be inaccurate is a neglect
of base-rate information.
 Base-rate information—information
about the likelihood of an event
 Diagnostic information—does an
individual case belong to a category?

26. Detecting Covariation
 Consider this example
 Testing a new drug, in hopes that it will cure
hepatitis
 Does taking the drug covary with a better
medical outcome?

27. Detecting Covariation
 Results
 70% of the patients taking the drug do recover
from the illness
 Uninterpretable
 If it turns out that the overall recovery rate is
70%, then our new drug is having no effect
whatsoever.

28. Detecting Covariation
 Interpretation
 We need to know the base rate
 How many are cured with no treatment
 How many more are cured with treatment

29. Detecting Covariation
 Kahneman and Tversky (1973)
 Base-rate information: 70 lawyers and 30
engineers
 Diagnostic information (engineering):
“likes carpentry, sailing, math puzzles;
dislikes politics”

30. Detecting Covariation
 The base-rate with no diagnostic
information = base rate
 The base rate is not neglected!
 Base-rate and diagnostic information =
diagnostic information.
 The base rate is neglected!

31. Detecting Covariation
Is Tom an engineer? Does Tom resemble an engineer?
Representativeness heuristicWhat percentage are engineers?
Attend to base rate Base-rate neglect

32. Assessing the Damage
 Imagine your friend has a system for
playing the lottery
 What if she tells you it only worked the last
time she played or
 She tells you it worked the last ten times she
played
 Which do you believe?
 Data set size and drawing conclusions
about a new category: One time might be
lucky; ten times is likely to be true.

33. Assessing the Damage
 Dual-process models
 System 1 refers to thinking that is fast,
automatic, and uses heuristics
 System 2 refers to thinking that is slower,
effortful, and more likely to be correct

34. Assessing the Damage
 Whether System 1 or System 2 is used
depends on the context of the decision
 How much time is available for the decision?
 How much attention and working memory are
available?
 And how the problem is presented
 What format are the data in?
 Are statistical concepts primed?

35. Assessing the Damage
 Emphasizing chance cues statistical
reasoning
 A story about a restaurant assessment based
on a single meal chosen by one person
 Informed assessment?
 Now imagine that the person dropped his or
her pencil on the menu to pick that meal
 Informed assessment?

36. Assessing the Damage
 Background knowledge increases the
likelihood that participants will pay
attention to base rates
 For instance, when predicting whether a
particular student will pass an exam,
participants do pay attention to the base-rate
information that only 30% of students pass
the exam

37. Assessing the Damage
37

38. Assessing the Damage
 Training can influence the likelihood of
reasoning with System 2
 For instance, participants can be trained that
large samples of data are more reliable than
small samples
 Taking a statistics class also improves
reasoning when sample size is important

39. Confirmation and Disconfirmation
 Deduction start with general premises
and ask what follows
 If you believe that red wine gives you
headaches, what follows from this?
 If relationships based on physical attraction
never last, what follows from this?

40. Confirmation and Disconfirmation
 Rooster wants to prove his crowing
causes the sun to rise
 Confirming evidence: every day the
rooster crows, and the sun rises
 Disconfirming evidence: one day he must
not crow and see what happens

41. Confirmation and Disconfirmation
 Confirmation bias—more responsive to
evidence that confirms one’s beliefs and
less responsive to evidence that
challenges one’s beliefs

42. Confirmation and Disconfirmation
 In a classic demonstration of confirmation bias,
Wason (1966) presented sequences like “2-4-6”
 Several minutes to figure out rule (ascending
numbers two apart)
 They only sought confirming evidence
 Did not seek disconfirming evidence
 A few did discover the rule
 Sought disconfirming evidence

43. Confirmation and Disconfirmation
 Selective Memory.
 Gamblers betting on a football game
 Wins are confirming evidence
 Losses are remembered as near-wins

44. Confirmation and Disconfirmation
 Belief perseverance is a tendency to
continue endorsing a belief even when
evidence has completely undermined it

45. Confirmation and Disconfirmation
 Assigned to good or bad groups
 Told about assignment
Bad judgers Good judgers
Ability to judge
whether authentic
Bad Good
Self-ratings of
social sensitivity
Low High

46. Logic
 Categorical
syllogisms logical
arguments containing
two premises and a
conclusion
 Syllogisms （三段論
） can be valid or
invalid

47. Logic
 Is this syllogism
valid?
 All P are M.
 All S are M.
 Therefore, all S are P.
 In concrete terms:
 All plumbers 水電工
are mortal 凡人 .
 All sadists 虐待狂 are
mortal.
 Therefore, all sadists
are plumbers.

48. Logic
 The errors people make on syllogisms
tend to fall into predictable categories
 One pattern is belief bias—if the
syllogism’s conclusion is something
people already believe to be true, they are
more likely to judge the conclusion as
following from the premises

49. Logic
 Low-level matching strategy between the
words in the premises and those in the
conclusions (the atmosphere effect)
 Some A are not X.
 Some B are not X.
 Therefore, some A are not B. (invalid)

50. Logic
 A conditional statement
 If X, then Y.
 If antecedent, then consequent

51. Logic
 modus ponens, affirming the antecedent
 If P is true, then Q is true.
 P is true.
 Therefore, Q must be true.
 Easiest form of logic

52. Logic
 modus tollens, denying the consequent
 If P is true, then Q is true.
 Q is false.
 Therefore, P must be false.
 More difficult

53. Logic
 Two common errors are affirming the
consequent
 If P is true, then Q is true.
 Q is true.
 Therefore, P must be true. (invalid)
 And denying the antecedent
 If P is true, then Q is true.
 P is false.
 Therefore, Q must be false. (invalid)

54. Logic
 If P is true, then Q is true.
P true P no true
Q true Modus ponens Illogical
Q not true Illogical Denial of the
consequent

55. Logic
 If P is true, then Q is true.
Conditional statement Type of reasoning
P true, Q true Modus ponens
P not true, Q not true Denial of the antecedent
Q true, P true Affirmation of the consequent
Q not true, P not true Modus tollens

56. Logic

57. Logic
 For both syllogisms
and conditional
statements, errors are
more likely when
 Negatives are involved
 The terms are abstract
(e.g., letters) and not
concrete

58. Logic
 Wason’s four-card task
 “If a card has a vowel on one side, then it must
have an even number on the other side”
 Which cards must be turned over to test this
rule?

59. Logic
4% of people

60. Logic
A more concrete example
“If a person is drinking beer, then the
person must be over 19 years of age.”

61. Logic
73% of participants

62. Logic
 Why are some versions of the four-card problem
difficult and others easy?
 Evolutionary psychologists suggest people can
“detect cheaters” who are not following rules of
social interaction

63. Logic
 Alternatively, a pragmatic reasoning schema
may help explain the ease
 These schemas involve “permission” or “cause
and effect” relations

64. Logic
 Problem: “If a form says ‘entering’ on one side,
then the other side must include ‘cholera.’”

65. Logic
 Permission schema
 “If a passenger wishes to enter the country, he
or she must first receive a cholera inoculation.”

66. Logic
 Necessary condition
 “If Jacob passed his driver’s test, then it’s
legal for him to drive.”
 Sufficient condition
 “If Solomon is eligible for jury duty, then he is
over 21.”

67. Logic
 Summary of logic
 People commonly rely on reasoning
strategies that are different from the principles
of formal logic
 Some of these principles are simple, such as
the “matching strategy”
 Others are more sophisticated, such as a
“permission schema,” but may only be
triggered under the right circumstances

68. Decision Making
 UtilityTheory
 Expected value = (probability of a particular
outcome) x (utility of the outcome)

69. Decision Making
 Many of our decisions follow the principle
of utility maximization, or choosing the
option with the greatest expected value

70. Decision Making
 However, many decisions do not follow
this principle
 For instance, consider the following
problem, as framed either in terms of lives
saved or lives lost

71. Decision Making

72. Decision Making
 Framing changes the choices
 Program A if the problem is “positively framed”
in terms of lives saved
 Program B if the problem is “negatively
framed” in terms of lives lost
 Identical utility

73. Decision Making

74. Decision Making
Risk-seeking
Risk-averse

75. Decision Making
To which parent would you award full child custody?

76. Decision Making
To which parent would you deny full child custody?

77. Decision Making
 An alternative view is known as reason-
based choice, the idea that people make
a decision only when they detect what
they believe to be a persuasive reason for
making that choice

78. Decision Making

79. Decision Making
 Reason-based choice
 Scenario A—there is only one choice (the
Sony)
 Scenario B—there are two choices

80. Decision Making
80
Number of choices increases
the sure choice

81. Decision Making
 The orbitofrontal
cortex is essential for
evaluation of somatic
markers
 Patients with damage
will make risky
decisions

82. Decision Making
 Emotions play a role in decision making, through
what might be called affective heuristics
 For instance, decisions that involve assessing
risk may depend on the feeling of dread of an
undesirable outcome, or anticipating the feeling
of regret for having made the wrong choice
 Note that the latter involves predictions about
our future emotions, which are not necessarily
accurate

83. Decision Making
People overestimate
their future feelings
83

84. Decision Making
 Decision making and happiness
 Unable to forecast our future feelings
 Would be better off having others make our choices
 We end up “stumbling on happiness”
 We end up stressed by the “paradox of choice”

85. Chapter 11 Questions

86. 1. The fact that people report motor-vehicle
deaths as more common than diabetes
and homicides as more common than
stomach cancer reflects which of the
heuristics?
a) simulation heuristic
b) anchoring heuristic
c) availability heuristic
d) representativeness heuristic

87. 2. Which of the following is TRUE of
covariation?
a) A negative covariation indicates that there
is no relationship between two variables.
b) People tend to underestimate covariation
when they have theories about the
relationship between two variables.
c) Covariations are “all-or-none” and cannot
vary in strength.
d) Illusory covariations sometimes generate
prejudice toward groups of people.

88. 3. Which of the following is FALSE regarding
confirmation bias?
a) It works to bring our recollections into line
with our expectations.
b) It makes people more alert and
responsive to evidence that confirms their
beliefs than to challenging evidence.
c) Its effects are usually offset by our
general ability to think about covariation.
d) It makes us unlikely to seek
counterexamples.

89. 4. Poor diagnostic reasoning and illusory
correlations have been documented in all
of the following cases EXCEPT
a) individuals with considerable experience
in the domain being judged.
b) participants who have been offered cash
bonuses for accurate performance.
c) individuals for whom the stakes are very
high (e.g., doctors and financial advisors).
d) All of the above individuals demonstrate
these errors.

90. 5. According to the dual-process model of
reasoning, one mode of thought is ___,
while the other mode of thought is ___.
a) association driven; speedy
b) automatic; effortful
c) slower; effortful
d) automatic; effortless

91. 6. In the study in which people were asked to judge
their social sensitivity after being given false-
positive or negative feedback (but then debriefed),
participants were clearly influenced by
a) views they had of themselves before the
experiment.
b) the feedback they had been given, even though
they knew it was false.
c) the feedback they had been given, but only if they
had forgotten the debriefing that undermined this
feedback.
d) a memory search done after debriefing to help
them disconfirm the false feedback.

92. 7. In the context of a syllogism, what is a
matching strategy?
a) If the two premises match each other, the
conclusion is accepted.
b) If the conclusion matches the premises in
wording and structure, it is accepted.
c) Statements with the same structure are
all seen as identical.
d) People accept syllogisms when the
conclusions match their beliefs.