Heuristics & Biases:
The Anchoring & Adjustment
& Availability Heuristics
Psychology 466: Judgment & Decision Making
Instructor: John Miyamoto
10/13/2015: Lecture 03-1
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Outline
• Briefly discuss this week's readings
• Summary re Linear Judgment Models
• Overview of the Heuristics & Biases Movement
• Anchoring & Adjustment Heuristic
Lecture probably
ends here
• Availability Heuristic
Psych 466, Miyamoto, Aut '15
Reading from Smart Choices
2
Readings from Smart Choices for Week 3
• Smart Choices
Ch 1 (Making smart choices)
Ch 10 (Psychological traps)
• Chapter 1 is an introduction to practical decision making
• Chapter 10 is a quick survey of how heuristic reasoning can
negatively impact practical decision making.
Psych 466, Miyamoto, Aut '15
Readings from HD and TFS
3
Readings from HD and TFS for Week 3
• Hastie & Dawes (HD)
Ch 4: Anchoring and adjustment;
Ch 5: Judging heuristically (availability)
• Kahneman, Thinking, Fast and Slow (TFS), pp. 109 - 146
Ch 10: The law of small numbers;
Ch 11: Anchors;
Ch 12: The science of availability;
Ch 13: Availability, emotion and risk
Psych 466, Miyamoto, Aut '15
Relevant (but Not Required) Reading re Availability
4
Relevant (but Not Required) Reading
I will be discussing the following papers in lecture. You will be
responsible for what is discussed in lecture, but not the details from
the papers.
♦
Ross, M., Sicoly, F. (1979). Egocentric biases in availability and
attribution. Journal of Personality and Social Psychology, 37, 322-336.
Distributed as a pdf file on the course website.
♦
Schwarz, N., Bless, H., Strack, F., Klump, G., Rittenauer-Schatka, H., &
Simons, A. (1991). Ease of retrieval as information: Another look at the
availability heuristic. Journal of Personality and Social Psychology, 61(2),
195-202. Distributed as a pdf file on the course website.
Psych 466, Miyamoto, Aut '15
Comment re Part I of TFS
5
Kahneman, Thinking, Fast and Slow
Part I. Two Systems
1. The Characters of the Story
2. Attention and Effort
3. The Lazy Controller
4. The Associative Machine
5. Cognitive Ease
6. Norms, Surprises, and Causes
Assigned Weeks 1 - 2
but NO LECTURES
up to now.
• At least skim it to see
the assumptions re
cognitive processes.
• Your understanding
will grow over time.
7. A Machine for Jumping to Conclusions
8. How Judgments Happen
9. Answering an Easier Question
Psych 466, Miyamoto, Aut '15
Remarks re Linear Judgment Models
6
Importance of Linear Models in the Psychology of Judgment
• 1960 – 1980: Provided strong evidence that human judgment
had difficulty processing complex information.
♦
Gave momentum to the heuristics & biases movement.
• 1990 – present: Continued study of linear judgment models
provides evidence for the value of heuristic reasoning.
♦
Example: The less-is-more effect.
Psych 466, Miyamoto, Aut '15
Accuracy-Effort Tradeoff (Diagram)
7
Accuracy-Effort Tradeoff
Method 1:
Multiple regression applied
to existing data.
Accuracy High
Effort High
Method 2:
Multiple regression applied
to a judge’s predictions
Method 3:
Importance weighting method
Method 4: Unit weighting model
Method 0: Intuitive judgment
(holistic judgment).
Psych 466, Miyamoto, Aut '15
Accuracy Low
Effort Low
Same Slide with Note re Less-Is-More Effect
8
Accuracy-Effort Tradeoff
Method 1:
Multiple regression applied
to existing data.
Method 2:
Multiple regression applied
to a judge’s predictions
Method 3:
Importance weighting method
Accuracy High
Effort High
Less-Is-More effect contradicts
the claim that there is an
accuracy-effort tradeoff.
(Gigerenzer & ABC Group)
Method 4: Unit weighting model
Method 0: Intuitive judgment
(holistic judgment).
Psych 466, Miyamoto, Aut '15
Accuracy Low
Effort Low
xx
9
Heuristics & Biases Movement
• Linear judgment models – part of the critique of human
judgment. Not usually regarded as part of the heuristics and
biases movement.
Heuristics & Biases Movement (H&B movement)
• Claim: Human cognition does not follow the pattern
of a rational agent model.
♦
(Rational model = expected utility theory & Bayesian decision model)
• Claim: Human reasoning uses heuristics that are often
effective, but heuristics can lead to systematic errors.
• Claim: Understanding the cognitive mechanism will lead
us to understand why people use the heuristics that they use.
Psych 466, Miyamoto, Aut '15
Digression: What is a Heuristic?
10
What is a Heuristic?
A heuristic is a reasoning strategy that is used to solve a problem,
make a decision or form a judgment about something.
◊
Original meaning:
A heuristic is a strategy that leads to insight, discovery and learning.
Examples
• To decide whether Option A is better than Option B,
assume that various specific situations prevail - is A
better than B in these situations?
• To decide whether Option A is better than Option B,
ask people who chose A how they feel about their choice?
Do the same for Option B.
Psych 466, Miyamoto, Aut '15
Same Slide with Expanded Description of Heuristic Strategies
11
What is a Heuristic?
A heuristic is a reasoning strategy that is used to solve a problem,
make a decision or form a judgment about something.
Heuristic reasoning strategies ....
♦
.... are often fast and effective,
♦
.... place low demands on cognitive resources.
♦
.... but they can lead to errors in particular situations.
• Observed patterns of errors can be used to diagnose
the heuristics that people use.
• Heuristic reasoning strategies are contrasted with optimal
computations and algorithms.
Psych 466, Miyamoto, Aut '15
Classroom Experiment: Rainfall in Miami
12
Classic Example of AA Strategy
Ask 50% of the class to close their eyes.
In a moment we will switch the group that
has their eyes open.
Psych 466, Miyamoto, Aut '15
Condition 1 of 2
13
Condition 1: AA Experiment
• Is the average yearly rainfall in Miami (Florida) greater
or less than 2 inches per year?
• Now write down your best guess as to the average
yearly rainfall in Miami.
Psych 466, Miyamoto, Aut '15
Switch
14
Switch Roles
• If you previously had your eyes open, close them now.
• If you previously had your eyes closed, open them now.
Psych 466, Miyamoto, Aut '15
Condition 2 of 2
15
Condition 2: AA Experiment
• Is the average yearly rainfall in Miami (Florida)
greater or less than 750 inches per year?
• Now write down your best guess as to the average
yearly rainfall in Miami.
Psych 466, Miyamoto, Aut '15
Open Your Eyes
16
Everyone Can Open Their Eyes
Psych 466, Miyamoto, Aut '15
Summary of Conditions 1 and 2
17
Questions Asked in Conditions 1 and 2
• Is the average yearly rainfall in Miami (Florida)
greater or less than ….
Condition 1
Condition 2
2 inches/year
750 inches/year
• Now write down your best guess as to the average
yearly rainfall in Miami.
JM: Write down students' estimates on the blackboard.
Psych 466, Miyamoto, Aut '15
Typical Finding for this Experiment
18
Typical Finding in Anchoring & Adjustment (AA) Experiment
Initially Consider
2 Inches as a Possibility
Final Estimate
Initially Consider
750 inches as a Possibility
<
Final Estimate
Final estimate is biased towards the "anchor"
(the number in the first question)
FYI: CurrentResults.com states that the average yearly rainfal in Miami is 61.9 inches
(157.2 cm). Average yearly rainfall in Seattle is 37.7 inches (95.8 cm).
Psych 466, Miyamoto, Aut '15
Anchoring and Adjustment Heuristic - Definition
19
Anchoring & Adjustment Heuristic
Step 1: Consider an initial estimate of the quantity you are trying
to judge. This is the “anchor.”
(People often know that this initial estimate isn't perfectly accurate.)
Step 2: Adjust the initial estimate in the direction that corrects for
assumed sources of error.
• Psychological Fact: Adjustments are typically too small!
• Result: Final judgment is overly influenced by the anchor,
i.e., the final estimate is biased towards the anchor.
Psych 466, Miyamoto, Aut '15
Example of the Anchoring and Adjustment Heuristic
20
Another Example of Anchoring-and-Adjustment
• Judgment Problem: Suppose you are trying to estimate how
many hours per week you will have to study if you take a
famously difficult course.
• People consider an initial estimate that is easy to produce.
♦
E.g., begin with an estimate of the hours per week of a typical course.
Call this the initial estimate.
• To produce a final estimate, adjust the initial estimate to a higher
based on the expected course difficulty.
• Prediction: This cognitive strategy will underestimate the hours
per week because the anchor is lower than the true number of
hours, and adjustments are typically too small.
Psych 466, Miyamoto, Aut '15
Other Examples of Anchoring and Adjustment
21
More Examples of Anchoring and Adjustment
• Example: Suppose a biased or unreliable news source tells you
that something extreme will happen, e.g, next year 50% of retail
banks will fail.
♦
You don’t trust this news source, so you adjust the estimate from 50% to
something you think is more realistic, but your adjustment will typically
be too small.
• Example: People anchor on their own opinions and values and
then adjust to take into account other people’s differences
(anchoring on ourselves).
Consequence: We tend to expect others to be more like
ourselves than they are.
Psych 466, Miyamoto, Aut '15
Experiment on False Consensus Effect
22
Lee Ross on the False Consensus Effect
Ross, L., Greene, D., & House, P. (1977). The “false consensus effect”: An egocentric bias in social perception
and attribution processes. Journal of Experimental Social Psychology, 13(3), 279-301.
Subjects were asked:
• Are you willing to do an outrageous act, e.g., wear a sandwich
board that says "Repent!" on campus?
• What percentage of other undergrads would agree to do the act?
Predicted %
Wear Sign Not Wear Sign
Subject’s Choice
n (%)
Yes Wear Sign
27 (51%)
58.3%
41.7%
Won’t Wear Sign 26 (49%)
29.7%
70.3%
Psych 466, Miyamoto, Aut '15
Typical Research Strategy in Heuristics & Biases Research
23
Typical Research Strategy in Heuristics & Biases Research
(a) Perform experiments that demonstrate reasoning errors.
(b) Use these errors to diagnose the heuristics that people
are using.
----------------------------------------------------------------------------Example:
• Experiment shows that people are influenced by an initial
anchoring estimate that is too high or too low.
• Use the demonstration of the influence of the anchor as
evidence that people use an anchoring and adjustment strategy.
Psych 466, Miyamoto, Aut '15
Cognitive Mechanisms that Produce Anchoring/Adjustment Bias
24
Why Are Estimates Biased Towards the Anchor?
Why are Adjustments Typically Too Small?
• Adjustments stop when you reach the range of values which
seem to be possible answers.
♦
E.g., I think that the rainfall in Miami must be between 20 - 100 inches
per year. If the anchor = 2 inches, I adjust until my estimate is over 20.
If the anchor is 750 inches, I adjust until my estimate is under 100.
• Cognitive laziness. I quickly terminate the process of finding
the "best" estimate.
• Priming: The anchor primes similar thoughts which influence
the production of the estimate.
♦
This idea fits best with findings like the false concensus effect.
Psych 466, Miyamoto, Aut '15
Overview of the Availability Heuristic Topic
25
Overview of Availability Heuristic
• Definition of the availability heuristic
• Standard memory model
• Different aspects of human memory process cause
different types of availability biases.
• Experiments reveal different aspects of the availability heuristic.
Psych 466, Miyamoto, Aut '15
What Is the Availability Heuristic?
26
What is the Availability Heuristic?
Availability heuristic – events are judged more probable if ...
(a) examples of similar events are easy to recall or
(b) examples of similar events easy to construct mentally
(in imagination).
Psych 466, Miyamoto, Aut '15
Same Slide with More Examples of Availability Heuristic
27
What is the Availability Heuristic?
• Availability heuristic – events are judged more probable if
examples of similar events are easy to recall or easy to
construct mentally (imagine).
• Example: How likely is it that the next U.S. presidential
election will produce a prolonged voting impasse like the
2000 presidential election (Bush versus Gore)?
• Example: How likely is it that the UW will be closed due to
snow this winter?
Psych 466, Miyamoto, Aut '15
Why Is the Availability Heuristic a Reasonable Judgment Procedure?
28
Why Is the Availability Heuristic a Reasonable Procedure?
• In general, frequently encountered events are easier to recall.
• The availability heuristic exploits the converse relationship:
Events that are easy to recall are thought to occur frequently.
Possibilities that are easy to imagine seem more likely.
Frequency of
Experience
Other Factors
Availability
of Memory
for an Event
Learning
Psych 466, Miyamoto, Aut '15
Availability
of Memory
for an Event
Judged
Frequency
of
Experience
Judgment of Likelihood
Standard Memory Model (Diagram)
29
Examples from Plous (The Psychology of Judgment and Decision Making)
• Which is a more likely cause of death in the United States:
being killed by falling airplane parts or being killed by a shark?
♦
In the United States, the chance of dying from falling airplane parts is 30
times greater than dying from a shark attack.
♦
Because shark attacks receive more publicity, information about shark
attacks is more readily available.
• Which claims more lives in the United States:
lightning or tornadoes?
♦
More Americans are killed annually by lightning than by tornadoes.
♦
Because tornadoes receive more publicity than occasional lightning
strikes, the most common answer is tornadoes.
Psych 466, Miyamoto, Aut '15
Another Example
30
Standard Memory Model
control processes
Working Memory
Sensory
Registers
External
Stimulus
Visual
Auditory
Haptic
Gustatory
Olfactory
Control Processes
Rehearsal
Coding
encoding
Long-Term
Memory
Memory Traces
Episodic
Semantic
Perceptual
Procedural
Symbol and Image
Manipulation
Information Processing
Strategies
retrieval
Cognitive Toolbox
Judgment Strategies
Decision Strategies
Heuristics
Influence of Availability
• Availability biases are the consequence of non-frequency
factors that influence memory encoding, retrieval, and
mental construction.
Psych 466, Miyamoto, Aut '15
Briefly Show Next Slide – A Related But
Different Diagram for the Standard Memory Model 31
H&D
Fig. 1.1
Sensory Input Buffers
Working Memory
Central Executive
Phonological
Buffer
Goal
Stack
Visuospatial
Buffer
Long-Term Memory
An alternative diagram for the standard memory model.
The preceding slide and the current slide are two different
versions of the same idea. The preceding slide emphasizes the
role of encoding and retrieval processes.
Psych 466, Miyamoto, Aut '15
Return to Previous Standard Memory Model with Color Emphasis
32
Standard Memory Model
control processes
Working Memory
Sensory
Registers
External
Stimulus
Visual
Auditory
Haptic
Gustatory
Olfactory
Control Processes
Rehearsal
Coding
encoding
Long-Term
Memory
Memory Traces
Episodic
Semantic
Perceptual
Procedural
Symbol and Image
Manipulation
Information Processing
Strategies
retrieval
Cognitive Toolbox
Judgment Strategies
Decision Strategies
Heuristics
Influence of Availability
• Availability biases are the consequence of non-frequency
factors that influence memory encoding, retrieval, and
mental construction.
Psych 466, Miyamoto, Aut '15
Return to Earlier Slide: Why Is Availability a Reasonable Heuristic? 33
Why Is the Availability Heuristic a Reasonable Procedure?
• In general, frequently encountered events are easier to recall.
• The availability heuristic exploits the converse relationship:
Events that are easy to recall are thought to occur frequently.
Possibilities that are easy to imagine seem more likely.
Frequency of
Experience
Other Factors
Availability
of Memory
for an Event
Learning
Psych 466, Miyamoto, Aut '15
Availability
of Memory
for an Event
Judged
Frequency
of
Experience
Judgment of Likelihood
Examples of Misperceived Risk from Scott Plous
34
Different Types of Availability Bias
• Biased exposure to events. Sampling bias
• Encoding and retrieval biases: Solo status and egocentric bias.
• Biases due to differential ease of retrieval or mental constructions
Psych 466, Miyamoto, Aut '15
Examples of Availability Bias Due to Biased Exposure
35
Availability Bias Due to Sampling Bias or Biased Exposure
• In 2002, which is more likely, death in a motor vehicle accident
or death from influenza or pneumonia?
♦
2002 motor vehicle deaths = 15.3 per 100,000;
Influenza/pneumonia deaths = 22.8 per 100,000
♦
TV coverage obviously emphasizes dramatic events and underrepresents
undramatic events. E.g., more Americans die from diabetes and stomach
cancer than from homicide and car accidents by a ratio of nearly 2:1.
• Clinical belief that child sexual molestors do not stop on their
own. People who are caught are much more likely to be serial
child molestors than a one-time child molestor.
Psych 466, Miyamoto, Aut '15
Hamill, Nisbett & Wilson Study – Insensitivity to Sampling Bias
36
People Tend to be Insensitive to Sources of Sampling Bias
Subjects viewed one of two video tapes that
shows an interview with a (fake) prison guard.
Hamil, Wilson, & Nisbett (1980).
♦
Humane tape: The prison guard is remarkably humane and
compassionate.
♦
Inhumane tape: The prison guard is brutal and cruel.
Condition 1: Subjects were given NO INFORMATION
about the typicality of the guard.
Condition 2: Subjects were told that the guard was
TYPICAL of guards at that prison.
Condition 3: Subjects were told that the guard was very
ATYPICAL.
Psych 466, Miyamoto, Aut '15
Diagram Showing the Experimental Design of Hamil, Wilson & Nisbett
37
People Tend to be Insensitive to Sources of Sampling Bias
After viewing the video, subjects are asked:
In general, what do you think prison guards are like?
Psych 466, Miyamoto, Aut '15
Results for Hamil, Wilson & Nisbett
38
People Tend to be Insensitive to Sources of Sampling Bias
predict humane
predict inhumane
predict humane
predict inhumane
predict humane
predict inhumane
Results showed little effect of the information about typicality.
• Subjects predicted that most guards were consistent with the
video tape (either humane or inhumane) without regard for his
typicality.
Psych 466, Miyamoto, Aut '15
Can We Resist Influence of Sampling Bias?
39
Tuesday, October 13, 2015: The Lecture Ended Here
Psych 466, Miyamoto, Aut '15
40
Remarks on Insensitivity to Sampling Bias or Exposure Bias
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 not a representative sampling of 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 know that these information sources are biased, but can we
correct for these biases or take them into account when forming
beliefs? Doubtful.
♦
Availability promotes influence of biased information.
♦
Anchoring and adjustment promotes influence of biased information.
Psych 466, Miyamoto, Aut '15
Continuation of the Remarks on this Slide
41
Remarks on Insensitivity to Sampling Bias or Exposure Bias
• Insensitivity to sampling bias (exposure bias) is not strictly a
cognitive bias.
♦
The world feeds us biased information, ....
♦
.... but we have difficulty taking this into account.
• Note that these results can result from a combination of
availability bias and anchoring and adjustment bias.
Psych 466, Miyamoto, Aut '15
Return to List of Different Types of Availability Bias
42
Different Types of Availability Biases
Biased exposure to events
Sampling bias
• Encoding and retrieval biases: Egocentric bias & solo status.
• Dramatic versus undramatic events
• Biases due to differential ease of mental constructions
Psych 466, Miyamoto, Aut '15
Encoding & Retrieval Biases – Famous Names x Men/Women
43