Heuristics & Biases:

Transcription

1 Heuristics & Biases: The Availability Heuristic and The Representativeness Heuristic Psychology 355: Cognitive Psychology Instructor: John Miyamoto 05/29/2018: Lecture 10-2 Note: This Powerpoint presentation may contain macros that I wrote to help me create the slides. The macros aren t needed to view the slides. You can disable or delete the macros without any change to the presentation.

2 Psych 355, Miyamoto, Spr 18 Heuristic Reasoning Strategies - Definition 2 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

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. Psych 355, Miyamoto, Spr '18 Main Claims of the Heuristics & Biases Movement 3

4 Main Claims of the Heuristics & Biases (H&B) Movement Daniel Kahneman & Amos Tversky 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. Psych 355, Miyamoto, Spr '18 Heuristic Reasoning Strategies - Definition 4

5 Some Heuristics in Inductive Reasoning Availability Representativeness Brief review from last week Main focus of today's lecture Anchoring & Adjustment Confirmation bias Focusing illusion Framing effects Mental accounting Not discussed in today's lecture There are many more heuristics than are listed here. Psych 355, Miyamoto, Spr '18 Availability Heuristic 5

6 Availability Heuristic Frequency of Experience Other Factors Availability of Memory for an Event Availability of Memory for an Event Judged Likelihood of a Similar Event Learning Judgment Availability heuristic events are judged more probable if similar events are easy to recall or easy to imagine. Perceived likelihood of events are biased when "other factors" strongly influence the availability of a memory Psych 355, Miyamoto, Spr '18 Same Slide - No Grey Barriers 6

7 Availability Heuristic Frequency of Experience Other Factors Availability of Memory for an Event Availability of Memory for an Event Judged Likelihood of a Similar Event Learning Judgment Availability heuristic events are judged more probable if similar events are easy to recall or easy to imagine. Perceived likelihood of events are biased when "other factors" strongly influence the availability of a memory Psych 355, Miyamoto, Spr '18 Sampling Bias in Public Media 7

8 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. Return to the Diagram of the Availability Heuristic & List of Other Factors Psych 355, Miyamoto, Spr '18 8

9 Other Factors that Influence the Availability of Events 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. Psych 355, Miyamoto, Spr '18 Summary re the Availability Heuristic 9

10 Psych 355, Miyamoto, Spr '18 Representativeness Heuristic 10 Summary re the Availability Heuristic Judging probability in terms of availability is a heuristic. It is generally a reasonable way to estimate likelihood, but it can lead to certain systematic errors. Factors that are not related to experienced frequency can make make particular events more available. E.g., the perceived probability of being killed by a random crazy person will tend to be exaggerated if biased news and cognitive biases make this kind of event more available than more mundane events.

11 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 '18 Example of Jim: An Athletic, Muscular & Competitive Guy 11

12 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? a) Jim is a professional athlete. b) Jim is a lawyer or financial analyst. This response is predicted by the Representativeness Heuristic This is the better bet. 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. Psych 355, Miyamoto, Spr '18 Return to Slide with Diagram of Representativeness Heuristic

13 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/likes flashy things. Is he... a professional athlete? a lawyer or financial analyst? Jim is similar to a stereotype. Jim is less similar to the stereotype. Judging probability based on the similarity to a stereotype overlooks the equally relevant base rate information: There are many more lawyers and financial analysts than professional athletes. Psych 355, Miyamoto, Spr '18 Intro to the Lawyer/Engineer Problem 13

14 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 30 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 70 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 '18 14

15 Results re Lawyer/Engineer Problem Probability of "engineer" was rated to be about the same in the low and high base rate conditions. (Subjects exhibit 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 Psych 355, Miyamoto, Spr '18 Why Do People Ignore Base Rates? The Representativeness Explanation 15

16 Why Do People Often Ignore Base Rates? The Representativeness Heuristic: People judge probability based on the similarity of the current case to a stereotype. (a) Jack is equally similar to a typical engineer in the low and high base rate conditions. (b) 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 '18 16

17 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. Psych 355, Miyamoto, Spr '18 Criticism of Goldstein s Description of the Lawyer/Engineer Problem 17

18 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. If subjects were taking account of the base rate, they would state a higher probability that Jack is an engineer in the 70/30 condition than in the 30/70 condition. Knowing only the result for the 70:30 condition does not establish that subjects ignore base rates. See Goldstein p Psych 355, Miyamoto, Spr '18 Conjunction Fallacies 18

19 Conjunction Fallacies The Famous Linda Problem 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 anti-nuclear demonstrations. F: Judge the probability that Linda is a feminist. T: Judge the probability that Linda is a bank teller. F & T: Judge the probability that Linda is a feminist and a bank teller. Probability Theory: P(F) P(F & T), P(T) P(F & T) Typical Judgment: P(F) > P(F & T) > P(T) This is the typical pattern of a conjunction fallacy. Why Are Conjunction Fallacies Psychologically Interesting? Psych 355, Miyamoto, Spr '18 19

20 Why Conjunction Fallacies Are Psychologically Interesting? Conjunction fallacies strongly support the claim: Human reasoning with uncertainty violates principles of probability theory. Human reasoning with uncertainty is based on a various heuristics the conjunction fallacy is caused by the use of a representativeness heuristic. Two Question Regarding Conjunction Fallacies: What is wrong with the judgment pattern: P(F) > P(F & T) > P(T)? Why do people's judgments have this pattern? Psych 355, Miyamoto, Spr '18 Probability & the Set Inclusion Principle 20

21 Tuesday, 29 May, 2018: The Lecture Ended Here Psych 355, Miyamoto, Spr '18 21