Transcript
© 2010 by W. W. Norton & Co., Inc.
Judgment and Reasoning
Chapter 11Lecture Outline
Chapter 12: Judgment and Reasoning
Lecture OutlineJudgment HeuristicsAnchoringDetecting CovariationAssessing the DamageConfirmation and DisconfirmationLogicDecision Making
Judgment Heuristics
Induction（歸納） is a pattern of reasoning in which one seeks to draw general claims from specific bits of evidenceBased 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?
Judgment Heuristics
Heuristic （捷思）Reasonably efficient and accurate Gain efficiency lose accuracy
Judgment heuristics includeAttribute substitutionAvailability heuristicRepresentativeness heuristic
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
Judgment Heuristics
Ease of reading = author intelligence
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.
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?
Judgment Heuristics
The availability heuristic More words that begin with “R”
RealityMore words with “R” in the third position,But words that begin with “R” are easier to
bring to mind
Judgment Heuristics
The availability heuristic may lead us to believe that we always do the housework ourselves
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
Judgment Heuristics
Availability heuristicGroup 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?
Judgment Heuristics
Those that gave 6 examples judged themselves as more assertive
Easier to come up with 6 examples
Judgment Heuristics
The representativeness heuristic is another example of attribute substitution
Member Prototype Categoryresembles resembles
Judgment Heuristics
For instance, considerDo 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?
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.
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
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.
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?
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
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?
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.
Detecting Covariation
Confirmation biasMore responsive to evidence that confirms
one’s beliefsSimilar to overregularization by schemataEssentially we ignore disconfirming data
Detecting Covariation
Big dogs are viciousNotice examples that fit this pattern more
readily (biased attention)Will recall examples that fit the pattern more
readily (biased memory)
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?
Detecting Covariation
Consider this exampleTesting a new drug, in hopes that it will cure
hepatitis Does taking the drug covary with a better
medical outcome?
Detecting Covariation
Results70% 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.
Detecting Covariation
InterpretationWe need to know the base rate
How many are cured with no treatment How many more are cured with treatment
Detecting Covariation
Kahneman and Tversky (1973) Base-rate information: 70 lawyers and 30
engineers Diagnostic information (engineering):
“likes carpentry, sailing, math puzzles; dislikes politics”
Detecting Covariation
The base-rate with no diagnostic information = base rateThe base rate is not neglected!
Base-rate and diagnostic information = diagnostic information.The base rate is neglected!
Detecting Covariation
Is Tom an engineer? Does Tom resemble an engineer?
Representativeness heuristicWhat percentage are engineers?
Attend to base rate Base-rate neglect
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 orShe tells you it worked the last ten times she
playedWhich 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.
Assessing the Damage
Dual-process modelsSystem 1 refers to thinking that is fast,
automatic, and uses heuristicsSystem 2 refers to thinking that is slower,
effortful, and more likely to be correct
Assessing the Damage
Whether System 1 or System 2 is used depends on the context of the decisionHow 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?
Assessing the Damage
Emphasizing chance cues statistical reasoningA 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?
Assessing the Damage
Background knowledge increases the likelihood that participants will pay attention to base ratesFor 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
Assessing the Damage
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Assessing the Damage
Training can influence the likelihood of reasoning with System 2For 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
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?
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
Confirmation and Disconfirmation
Confirmation bias—more responsive to evidence that confirms one’s beliefs and less responsive to evidence that challenges one’s beliefs
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
Confirmation and Disconfirmation
Selective Memory.Gamblers betting on a football game
Wins are confirming evidence Losses are remembered as near-wins
Confirmation and Disconfirmation
Belief perseverance is a tendency to continue endorsing a belief even when evidence has completely undermined it
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
Logic
Categorical syllogisms logical arguments containing two premises and a conclusion
Syllogisms（三段論） can be valid or invalid
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.
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
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)
Logic
A conditional statement If X, then Y. If antecedent, then consequent
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
Logic
modus tollens, denying the consequent If P is true, then Q is true.Q is false.Therefore, P must be false.
More difficult
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)
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
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
Logic
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
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?
Logic
4% of people
Logic
A more concrete example
“If a person is drinking beer, then the person must be over 19 years of age.”
Logic
73% of participants
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
Logic
Alternatively, a pragmatic reasoning schema may help explain the ease
These schemas involve “permission” or “cause and effect” relations
Logic
Problem: “If a form says ‘entering’ on one side, then the other side must include ‘cholera.’”
Logic
Permission schema “If a passenger wishes to enter the country, he
or she must first receive a cholera inoculation.”
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.”
Logic
Summary of logicPeople 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
Decision Making
UtilityTheory Expected value = (probability of a particular
outcome) x (utility of the outcome)
Decision Making
Many of our decisions follow the principle of utility maximization, or choosing the option with the greatest expected value
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
Decision Making
Decision Making
Framing changes the choicesProgram A if the problem is “positively framed”
in terms of lives savedProgram B if the problem is “negatively
framed” in terms of lives lost Identical utility
Decision Making
Decision Making
Risk-seeking
Risk-averse
Decision Making
To which parent would you award full child custody?
Decision Making
To which parent would you deny full child custody?
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
Decision Making
Decision Making
Reason-based choiceScenario A—there is only one choice (the
Sony)Scenario B—there are two choices
Decision Making
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Number of choices increases the sure choice
Decision Making
The orbitofrontal cortex is essential for evaluation of somatic markers
Patients with damage will make risky decisions
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
Decision Making
People overestimate their future feelings
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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”
Chapter 11 Questions
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
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.
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.
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.
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
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.
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.
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