1. Heuristics & Biases: The Availability Heuristic and The Representativeness Heuristic
Psychology 355: Cognitive Psychology Instructor: John Miyamoto 5/31/2016: Lecture 10-2
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2. Lecture probably ends within this topic
Outline
Reminder about the heuristics & biases program in judgment and decision making (JDM)
The availability heuristics - definition and examples
The representativeness heuristic
Definition
Some examples
Discussion of why people tend to judge probability based on similarity
Lecture probably ends within this topic
Heuristic Reasoning Strategies - Definition
Psych 355, Miyamoto, Spr ‘16

3. Heuristic Reasoning Strategies
Heuristic reasoning strategies – reasoning strategies that are useful because they are easy and generally effective, even though they can sometimes lead to errors.
Main Claims of the Heuristics & Biases Movement
Psych 355, Miyamoto, Spr '16

4. Main Claims of the Heuristics & Biases (H&B) Movement
Human cognitive processes do not follow the pattern of a rational model.
(Rational model = expected utility theory & Bayesian decision model)
Human decision making uses heuristic strategies. Heuristic reasoning strategies ....
.... are often fast and effective,
.... place low demands on cognitive resources.
.... but they can lead to errors in particular situations.
Heuristic Reasoning Strategies - Definition
Psych 355, Miyamoto, Spr '16

5. Some Heuristics in Inductive Reasoning
Today's lecture
Availability
Representativeness
Anchoring & Adjustment
Confirmation bias
Focusing illusion
Framing effects
Mental accounting
More heuristics that have been proposed than are listed here.
Availability Heuristic
Psych 355, Miyamoto, Spr '16

6. Availability Heuristic
Frequency of Experience
Other Factors
Availability of Memory for an Event
Learning
Judged Likelihood of a Similar Event
Judgment
Availability heuristic – events are judged more probable if similar events are easy to recall or easy to imagine.
In general, frequently encountered events are easier to recall.
The availability heuristic exploits the converse of this relationship: Events that are easy to recall are thought to be frequent in occurrence.
Availability heuristic causes biased probability judgments when other factors that influence availability are not taken into account.
Psych 355, Miyamoto, Spr '16
Same Slide Without Emphasis Rectangles

7. Availability Heuristic
Frequency of Experience
Other Factors
Availability of Memory for an Event
Learning
Judged Likelihood of a Similar Event
Judgment
Availability heuristic – events are judged more probable if similar events are easy to recall or easy to imagine.
In general, frequently encountered events are easier to recall.
The availability heuristic exploits the converse of this relationship: Events that are easy to recall are thought to be frequent in occurrence.
Availability heuristic causes biased probability judgments when other factors that influence availability are not taken into account.
Psych 355, Miyamoto, Spr '16
Availability Experiment: Lists of Famous & Non-Famous Names

8. Condition I: Famous Male Non-Famous Female
Availability Bias Due to Ease of Encoding Famous/Non-Famous Names x Male/Female
Condition I: Famous Male Non-Famous Female
Bill Clinton Tom Hanks Michael Jordan
Mary Brooks Andrea Forbus Leanne Faris
Condition II: Famous Female Non-Famous Male
William Hale Murray Jencks Lionel Worley
Michelle Obama Angelina Jolie Sarah Palin
Subjects saw a list of names, one at a time, that mixed famous males with non-famous females, or vice versa. There were 18 famous and 19 non-famous names in the list.
Next: Same Slide with No Barriers & Results
Psych 355, Miyamoto, Spr '16

9. Results: Famous/Non-Famous Names x Male/Female
Condition I: Famous Male Non-Famous Female
Bill Clinton Tom Hanks Michael Jordan
Mary Brooks Andrea Forbus Leanne Faris
Condition II: Famous Female Non-Famous Male
William Hale Murray Jencks Lionel Worley
Michelle Obama Angelina Jolie Sarah Palin
Results:
Subjects reported more males if the males were famous;
Subjects reported more females if the females were famous.
Availability influences perceived frequency.
Reminder of Link to Memory Model
Psych 355, Miyamoto, Spr '16

10. Importance of "Other Factors" in Causing the Availability Heuristic
Frequency of Experience
Other Factors
Availability of Memory for an Event
Learning
Judged Likelihood of a Similar Event
Judgment
“Other Factors” that influence availability of a memory
Famous names are easy to encode and easy to retrieve.
Non-famous names are harder to encode and harder to retrieve.
Psych 355, Miyamoto, Spr '16
Experimental Demonstration of Egocentric Bias

11. Egocentric Bias (Example of Availability Heuristic)
Egocentric bias: People overestimate the proportion that they have contributed to a project or activity.
Ross & Sicoly (1979): Subjects were 37 married couples.
Working separately, husband and wife rated self and spouse for their work on 20 activities: making breakfast; cleaning dishes; cleaning house; making important decisions; ... ; causing arguments between themselves; making the house messy; irritating spouse.
primarily primarily husband wife
Psych 355, Miyamoto, Spr '16
How Are Responses Scored for Husband's and Wife's Perception of Contribution

12. Rating Procedure in Egocentric Bias Study
Husband and wife rated self and spouse for their work on 20 activities
primarily primarily husband wife
Subjects rated their responsibility on a line as shown above.
Husband's rating measured as distance from the right end; wife's ratings measured as distance from the left end.
If husband and wife have accurate perceptions of responsibility, the sum of their ratings should equal the length of the line.
Wife's Mark
Husband's Mark
Husband's Rating
Wife's Rating
Predicted Response Pattern If No Bias Existed
Psych 355, Miyamoto, Spr '16

13. Example: Suppose that Husband & Wife's Ratings Are Consistent With Each Other
Husband and wife agree as to contribution of each to a task like washing dishes:
primarily primarily husband wife
If husband and wife were not egocentric, the couple's ratings would sum to +100.
▐ + 25 in husband's scoring ▐ + 75 in wife's scoring
+100 total of husband & wife
_________________________
Predicted Response Pattern If Egocentric Bias Exists
Psych 355, Miyamoto, Spr '16

14. Example: Suppose that Husband & Wife's Ratings Are Inconsistent With Each Other
Husband and wife disagree about their contributions to washing dishes.
primarily primarily husband wife
If husband and wife are egocentric, the couple's ratings would sum to more than 100.
▐ + 48 in husband's scoring ▐ + 75 in wife's scoring
+123 total of husband & wife
_________________________
Results for Egocentric Bias Study
Psych 355, Miyamoto, Spr '16

15. Results for Egocentric Bias Study
The inconsistent pattern is typical: On many activities, ....
Ratings consistently summed to number greater than +100 across many activities, showing an excessive attribution of credit or blame to the self.
The result holds for both good things (wash the dishes) and bad things (buy unnecessary things).
Husband’s Rating + Wife’s Rating > 100
Conclusion re Egocentric Bias – Relation to Availability
Psych 355, Miyamoto, Spr '16

16. Importance of "Other Factors" in Causing the Availability Heuristic
Frequency of Experience
Other Factors
Availability of Memory for an Event
Learning
Judged Likelihood of a Similar Event
Judgment
Egocentric bias is probably due to the greater availability of self-actions than partner actions "Other Factors" = Greater Awareness of Self than of Other
Other Examples:
Self versus supervisor focus in attributing responsibility for BA thesis work.
Basketball players attributing responsibility for win or loss to actions of own team more than to actions of the other team.
Psych 355, Miyamoto, Spr '16
Sampling Bias in Everyday Media

17. Sampling Bias in Everyday Media
Biases in Information Sources
Biases in Availability
Biases in Perceived Likelihood of Events
Things we all know:
TV ads do not give an accurate picture of the value of products.
Political spin doctors are trying to manipulate our beliefs.
TV news is emphasizes dramatic events; it ignores undramatic events.
The portrayal of men/women, black/whites, rich/poor, gay/straight, on TV is not a representative presentation of these groups.
Our own experiences are not typical of everybody’s experience.
Etc.
We all know that these information sources are biased, but can we really correct for these biases when forming beliefs? Doubtful.
Insensitivity to sampling bias (exposure bias) is not strictly a cognitive bias. The world is biased, but we have difficulty taking this into account.
Psych 355, Miyamoto, Spr '16
Return to the Diagram of the Availability Heuristic & List of “Other Factors”

18. “Other Factors” that Influence the Availability of Events
Examples of “Other Factors”
Egocentric bias.
Dramatic events seem more common than non-dramatic events.
Biases in the media create biases in the availability of stereotypes.
Recent events seem more common than earlier events.
Anything that makes events easier to encode or retrieve can make the events seem more frequent than they are.
Conclude with remarks re the importance of probability judgment in decision making.
Tomorrow: Representativeness heuristic
Summary re the Availability Heuristic
Psych 355, Miyamoto, Spr '16

19. Summary re the Availability Heuristic
Judging probability in terms of availability is a heuristic.
I.e., it is generally a reasonable way to estimate likelihood, but it can lead to systematic errors.
Factors that are not related to experienced frequency can make make particular events very available.
E.g., the perceived probability of being killed by a random crazy person will tend to be exaggerated.
Definition of the Representativeness Heuristic
Psych 355, Miyamoto, Spr '16

20. Representativeness Heuristic
Event A is more representative than Event B
Event A is more probable than Event B
"more representative"
means
"more similar to a stereotype of a class or to a typical member of a class."
Representativeness Heuristic: Judge the probability of an event E by the representativeness of the event E.
We need some example to make this idea more clear (see next).
Psych 355, Miyamoto, Spr '16
Example of Jim: An Athletic, Muscular & Competitive Guy

21. Representativeness Heuristic – An Example
Question: Jim is tall and very muscular. He's also very competitive He drives an expensive car and wears flashy clothing Which is more probable?
Jim is a professional athlete.
Jim is a lawyer or financial analyst.
People predict that Jim is a professional athlete because Jim is similar to a stereotype of a professional athlete.
It is a better bet that Jim is a lawyer or financial analyst because there are many more lawyers and financial analysts than professional athletes.
This response is predicted by the Representativeness Heuristic
This is the better bet.
Return to Slide with Diagram of Representativeness Heuristic
Psych 355, Miyamoto, Spr '16

22. Representativeness Heuristic
Event A is more representative than Event B
Event A is more probable than Event B
Representativeness Heuristic: Events that are more representative are regarded as more probable.
Example: Jim is muscular/athletic/competitive.
Clarify meaning of “representativeness.”
a professional athlete?
a lawyer or financial analyst?
Is he .....
Jim is similar to a stereotype.
Jim is less similar to the stereotype.
Intro to the Lawyer/Engineer Problem
Psych 355, Miyamoto, Spr '16

23. Lawyer/Engineer Problem (K&T, 1973)
DESCRIPTION OF JACK: Jack is a 45-year-old man. He is married and has four children. He is generally conservative, careful, and ambitious. He shows no interest in political and social issues. (This description is designed to fit the stereotype of an engineer more than the stereotype of a lawyer.)
30:70 Condition: High Base Rate for Engineer If Jack's description were drawn at random from a set of lawyers and 70 engineers, what would be the probability that Jack is one of the engineers?
70:30 Condition: Low Base Rate for Engineer If Jack's description were drawn at random from a set of lawyers and 30 engineers, what would be the probability that Jack is one of the engineers?
Findings re Lawyer/Engineer Problem
Psych 355, Miyamoto, Spr '16

24. Results re Lawyer/Engineer Problem
Probability of "engineer" was rated to be about the same in the low and high base rate conditions (Insensitivity to Base Rate, a.k.a. Base Rate Neglect)
High base rate condition = 30:70 Condition Low base rate condition = 70:30 Condition
Probability theory implies that Jack is much more likely to be an engineer in the high base rate condition than in the low base rate condition.
Why do people ignore base rates? See next slide
Why Do People Ignore Base Rates? The Representativeness Explanation
Psych 355, Miyamoto, Spr '16

25. Why Do People Often Ignore Base Rates?
The Representativeness Heuristic: People judge probability based on the similarity of the current case to a stereotype.
Jack is equally similar to a typical engineer in the low and high base rate conditions.
People ignore the base rate because the base rate is irrelevant to the judgment of how similar Jack is to a typical engineer.
Probability theory shows that the base rate is very relevant to judging the probability that Jack is an engineer.
Cognitive theory shows that the base rate is often not psychologically relevant to judging the probability that Jack is an engineer.
When Does It Matter Whether People Ignore Base Rates?
Psych 355, Miyamoto, Spr '16

26. Tuesday, May 31, 2016: The Lecture Ended Here
Psych 355,, Miyamoto, Spr '16

27. When Does It Matter Whether People Ignore Base Rates?
Evidence shows that physicians sometimes overlook base rates when attempting to diagnose a disease.
Evidence suggests that investors are overly influenced by short-term information regarding the value of stocks.
Business decisions tend to be overly influenced by short-term trends.
Criticism of Goldstein’s Description of the Lawyer/Engineer Problem
Psych 355, Miyamoto, Spr '16

28. Criticism of Goldstein’s Description of the Lawyer/Engineer Problem
The Goldstein description of this study is inadequate because it does not contrast the 30:70 condition with the 70:30 condition. It only mentions the 70:30 condition.
The important finding is that subjects in the 30:70 and 70:30 conditions are equally confident that Jack is an engineer (subjects in the two conditions overlook the difference in the base rate).
Knowing only the result for the 70:30 condition does not establish that subjects ignore base rates.
See Goldstein p. 374.
Psych 355, Miyamoto, Spr '16
Explain Idea of a Regression Effect - What Is a Regression Effect?