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Jan Noyes
Professor of Human Factors Psychology
University of Bristol
http://human-factors.psy.bris.ac.uk/
Integrated Uncertainty Modelling for Decision Making Workshop
Outline
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Humans as information processors
Decision making as explained by reasoning
Risk perception
The study of human decision making over the decades
Influences on decision making
Summing up – how do humans make decisions
Conclusions especially with regard to uncertainty
Humans as ‘information processors’
Our strengths
Perception
The process of receiving information from the outside
world.
Note: humans are ‘furious’ pattern-matchers
Memory - an interesting paradox …
Humans have amazing memories but also severe
limitations on the amount of information they can
process at any one time, for example, short term
memory is fragile and limited, and effort is required to
retrieve information.
Year
Car
Registration
Colour
1947
Ford 8
ETA242
Black
1953
Morris Minor
RTT859
Blue
1957
Morris Minor
VOD236
Turquoise
1959
Ford Prefect
496FAF
Blue
1961
Ford Consul
848SPH
Navy Blue
1965
Morris Oxford
CWV695C
Navy/White
1972
Hillman Hunter
KPG974K
Metallic Red
1977
Renault 16
NDR697S
White
1980
Talbot Alpine
CAM687V
Navy Blue
1982
Vauxhall Cavalier
VPM495Y
Green
1985
Ford Granada
C708SPC
Maroon Red
1986
Ford Escort
D194KCV
Grey
1988
Vauxhall Cavalier
F413VCV
Blue
1990
Mazda 323 F
H896FGL
Red
1993
Citroen Zantia
K628PRL
Blue
1997
Renault Megane
P396RAF
Blue
2002
Renault Clio
WL51LUR
Metallic Green
Our weaknesses
Attention
We are poor at monitoring.
“There is no such thing as voluntary attention sustained
for more than a few seconds at a time.”
Quote from William James (1890)
Higher order (cognitive) processes
We are not good at some types of decision making, for
example, deductive reasoning.
Deductive reasoning
The process of reasoning from one or more premises
with regard to what is known, and upon which a logically
specific conclusion can be reached.
All A are B,
All B are C,
therefore, all A are C.
Inductive reasoning
Reasoning from specific facts or observations to a
general conclusion that may explain the facts, that is, it is
not possible to reach a logically certain conclusion.
All men are mortal,
therefore, Fred Bloggs is mortal.
Deductive versus Inductive reasoning
Deductive - logic, while Inductive - particular conclusions
are drawn from more general principles.
Inductive reasoning involves an element of
doubt/uncertainty.
If Alan is taller than Bill, and Bill is shorter than Chris, is
Alan taller than Chris?
Common mistakes
• Draw incorrect conclusions,
for example, if I take my umbrella, then it will rain.
• Reverse the propositions in the conditional statement,
for example, if the ‘plane will be diverted, then there is
fog.
• Confirmation bias (seek to confirm).
Wason’s 4-card problem
You have four cards with a letter on one side and a
number on the other.
E
F
4
7
“If a card has a vowel on one side, it will have an even
number on the other.”
Which two cards do you want to turn over to check
whether this rule is valid or not?
Drinking age rule
Drinking
a beer
Drinking
a coke
22 years
of age
16 years
of age
Which card or cards do you want to turn over to check
whether the ‘drinking age’ rule is valid or not?
Entering the country
Entering
In transit
Inoculated
against
cholera
& hepatitis
Inoculated
against
typhoid
The rule ‘people entering the country have been
inoculated against cholera’.
Is this valid or not?
Explanations
• People do not reason logically – they simply apply their
knowledge of the world – helps cope with uncertainty.
• Meaningful content – limits of working memory.
If correct, not an issue,
if incorrect, can lead to problems.
• Difficulties – representation, negation, language.
• Confirmation bias –
search for evidence that confirms our beliefs.
For example, Three Mile Island.
Three Mile Island, 1979
Decision making
Early models – based on Normative decision making
Break down decision problems.
• Do this by identifying the alternatives.
• Weigh the outcomes in terms of their usefulness (utility).
• Select the ‘best’ outcome.
Goal - to seek pleasure and avoid pain.
When decision making, we:
• seek to maximise pleasure (+ve utility)
• seek to minimise pain (-ve utility).
From Normative to Descriptive
In the 1970s, the basic UTs ‘failed’, because of the
subjective element in the observed behaviour of decision
makers.
There was seen a need to take into account human
irrationality and biases.
Hence, the Descriptive models appeared.
The Prisoner’s Dilemma
Suppose that two men have been arrested and they are
charged with a bank robbery. Each man is found to have
an unregistered firearm at the time of the arrest. The
police do not have conclusive evidence that the two men
actually robbed the bank, and need a confession from at
least one of the men in order to make a successful
prosecution.
The Dilemma
If neither confesses, they will be charged with
possessing an illegal firearm and jailed for a year.
If they both confess, they will each be given an
intermediate-length term of 10 years.
Further, the prisoner who confesses will be let off, while
the other will get the maximum sentence of 20 years.
Would you confess?
Prisoner A
Confess
Not Confess
Prisoner B
Confess
Not
Confess
Both get
10 years
A=0 years
B=20 years
A=20 years
B=0 years
Both get 1 year
Game theory
Suggests that much decision making is like playing a game
with the following features:
Minimax loss rule - minimise possibility of maximum loss
(20 years) - confess (possibility of 0 [or 10] years).
Maximin gain rule - maximise possibility of minimum gain
(least favourable outcome = 20 years) - don’t confess.
Maximax gain rule - maximise possibility of maximum gain confess.
Normative and Descriptive
Criticism of early (normative and descriptive) theories they often do not use problems and scenarios that are
realistic.
Solution – the Prescriptive models.
• These focus on how people should make decisions to
conform to the normative model.
• Still idealised, but taking into account, the real situation
often characterised by ambiguous and incomplete
information, limited time resources, and high stakes.
• This led to the development of naturalistic decision
making (NDM) prescriptive models in the 1990s.
Insights into NDM (complex decision making)
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Klein (1993) and Rasmussen (1993)
Focus on finding a course of action which works.
Assess situation and select course of action (experience
helps - become quicker and more accurate).
Act without considering all contingencies. Course of
action is not necessarily the best one - best one at that
point in time.
Choice is related to evaluation and mental construction
of problem.
Focus on relevant options rather than filtering out
unacceptable ones.
Putting the pressure on …
In a high workload/panic-type situation, what happens?
• Resort to automatic (skilled) behaviour, for example, use
of checklists will help to reduce memory load.
• High levels of attention can be sustained.
• Will become ‘tunnel-visioned’, for example, fixation in
terms of problem-solving.
Historical perspective - decision making
• Early decision theories based on (a) humans operate in
ideal circumstances, and (b) make optimal decisions.
• Recent work - we strive to make the ‘best’ decisions in
any given situation.
• Naturalistic theories are a mixture of different models
and strategies, and more suited to explaining decision
making in operational environments such as the flight
deck, fire-fighting/emergency services.
How do humans make decisions?
1. Satisficing
We do not consider all the options, but opt for the first
choice that ‘satisfies’ us, for example, working through a
long menu.
How do humans make decisions?
1. Satisficing
We do not consider all the options, but opt for the first
choice that ‘satisfies’ us, for example, working through a
long menu.
2. Heuristics and Biases
We do not apply logic but tend to resort to feelings …
For example,
All the families having exactly six children in a particular
city were surveyed. In 72 of the families, the exact order
of births of boys (B) and girls (G) was G B G B B G.
What is your estimate of the number of families surveyed
in which the exact order of births was B G B B B B?
3. Availability (Anchoring)
The extent to which information is available to us can
determine our decision making.
Influence of media and how available information is to
us. Evidence when there is a health scare, for example,
about the contraceptive pill.
Example:
What percentage of African countries are in the United
Nations?
3. Availability (Anchoring)
The extent to which information is available to us can
determine our decision making.
Influence of media and how available information is to
us.
Odds of dying ...
In a car crash: 5,000 to 1
From surgical complications: 80,000 to 1
In a ‘plane crash: 250,000 to 1
By falling out of bed: 2 million to 1
WINNING THE LOTTERY: 80 million to 1
4. Overconfidence
We tend to overvalue our judgement skills.
Example:
“Absinthe is a liqueur or a precious stone.”
4. Overconfidence
We tend to overvalue our judgement skills.
Example:
“Absinthe is a liqueur or a precious stone.”
5. The Gambler’s Fallacy
Luck will change, for example, have lost money on five
horse races, therefore, will win on the sixth race.
But, probability has no memory …
4. Overconfidence
We tend to overvalue our judgement skills.
Example:
“Absinthe is a liqueur or a precious stone.”
5. The Gambler’s Fallacy
Luck will change, for example, have lost money on five
horse races, therefore, will win on the sixth race.
But, probability has no memory …
6. Fallacy of Composition
Parts of the whole make up the whole, for example, the
‘horns/halo’ effect.
More evidence of plasticity
Order effects
How questions affect answers?
Q.1. Do you think a Communist country like Russia should
let American newspaper reporters come in and send
back to America the news as they see it?
Q.2. Do you think the USA should let Communist
newspaper reporters from their countries come in and
send back to their papers the news as they see it?
Results
Q.1. Do you think a Communist country like Russia should
let American newspaper reporters come in and send
back to America the news as they see it?
Q.2. Do you think the USA should let Communist
newspaper reporters from their countries come in and
send back to their papers the news as they see it?
Counterbalanced design - 50% had Q.1 first.
Q.1: 82% agreed when 1 first, 64% agreed when 2 first.
Q.2: 55% agreed when 1 first, 75% agreed when 2 first.
Pseudo-opinions
Which of the following statements most closely coincides
with your opinion of the Metallic Metals Act?
1. It would be a good move on the part of the USA.
2. It would be a good thing, but should be left to individual
states.
3. It is all right for foreign countries, but should not be
required here.
4. It is of no value at all.
Results
1. It would be a good move on the part of the USA. (15%)
2. It would be a good thing, but should be left to individual
states. (41%)
3. It is all right for foreign countries, but should not be
required here. (11%)
4. It is of no value at all. (3%)
No opinion (30%).
Inconsistency
Principles:
• Public officials should be chosen by majority vote.
• Every citizen should have an equal chance to influence
government policy.
• The minority should be free to criticize majority
decisions.
Derived statement:
“In a city referendum, only people who are well informed
about the problem being voted on should be allowed to
vote.”
Results
It was found that:
• 51% agreed with anti-democratic idea that only wellinformed should vote.
Similar study with taxpayers.
It was found that:
• 79% agreed that only taxpayers should vote.
Problems …
• Integration of information – problematic for us (attention
deficit).
• Resource limitations (memory) – perhaps cannot cope
with all the aspects involved.
• Prediction outcomes – create uncertainty, possibly
because of difficulties associated with integration.
• Language, for example, negatives, conditional clauses,
use of probability – poor understanding.
• Simple manipulations can change our decision making,
for example, switching the order of questions can
influence the answers.
• People when asked will often give answers.
• Generally, people exhibit inconsistency.
Summary: Making decisions
• Construction of a mental representation (story) – an
integration of available information, knowledge and
personal beliefs about the world.
• Assessment of the situation.
• Realistic settings – uncertain situations, incomplete, and
often, contradictory information, time pressure, delay in
feedback, shifting, and competing, goals, and changing
conditions.
• In terms of strategy, experiments at Bristol have shown
differences in how people perceive levels of risk
according to how information is presented.
Conclusions
We excel in situations which demand the use of
inductive reasoning (unlike machines/computers that can
programmed to carry out deductive reasoning).
It could be concluded that we do not use ‘knowledge’
optimally - we use ‘short cuts’ which guarantee solutions
(which are not necessarily the best) – the fast but frugal
heuristic.
In this sense, uncertainty is not a problem, because we
are not very efficient decision makers anyway.
Finally …
“Many people would sooner die than think. In fact they do.”
Bertrand Russell