Cognitive Psychology, 2nd Ed.
Chapter 14
Reasoning and Decision Making
Syllogistic Reasoning
Valid deductive conclusions necessarily
follow from the premises.
All A are B (All professors are birds)
All B are C (All birds are aliens)
All A are C (All professors are aliens)
Syllogistic Reasoning
Most syllogistic forms are invalid:
All A are B
Some B are C
Some A are C? Not necessarily!
No A are B
No B are C
No A are C? Not necessarily!
Cognitive Constraints
Working memory limits the number of
alternatives considered.
Illicit conversion: misinterpreting “All A
are B” to mean “All B are A.”
Belief bias: humans in diverse cultures
accept conclusions as valid when they
fit cultural beliefs.
Conditional Reasoning
(If P, then Q)
Affirming the antecedent (P)
Denying the consequent (not Q)
Denying the antecedent (not P)
Affirming the consequent (Q)
Modus Tollens—Denying the
Consequent
If a card has a vowel on one side, then
it has an even number on the other
side. 4% turn over the 7.
Catch the cheater in a social situation!
beer-16, beer-21, soda-16, soda-21
If the person is drinking beer, then she
is over 21.
beer soda 21 16
Expected Utility Theory
Bet 1: Win $8 with odds 1/3
$8 X 1/3 = $2.67
Bet 2: Win $3 with odds of 5/6
$3 X 5/6 = $2.50
Expected utility greater for Bet 1,
most people select Bet 2.
Subjective Utility Curve
Value (subjective utility) increases
slowly for gains.
Implication: Further and further gains,
don’t make people as happy as going
from zero to a small gain.
Subjective Utility Curve
Value (subjective utility) decreases
rapidly for losses but then begins to
level out.
Implication: Initial losses are the most
painful. Very heavy losses, on the other
hand, are tolerated better than one
might expect.
Stock Market Behavior
Buyer’s regret--reference point is often
lowered right after purchasing a stock,
increasing the perception of risk (paid $50,
but now only think it’s worth $45—a small
loss).
The buyer is risk averse and the small loss
looks too large to keep the stock in the
portfolio for long. Even a winning stock can
look too risky to keep.
A losing stock, on the other hand, puts one
into the risk tolerant region. Losers are held
too long.
Estimating Probabilities
Overestimates of low frequency events
(note: insurance premiums take into
account this error).
Underestimates of high frequency
events.
(note: works against those engaged in
risky behavior with high probability,
negative consequences).
Representativeness Heuristic
Typical events of a category are seen as
more probable (e.g., HTTHHT >
HHHTTT).
Law of small numbers—mistakenly
expect small samples to mirror
population statistics and the Gambler’s
Fallacy.
Conjunctive Fallacy: Pr (AB) > Pr (A)
Availability Heuristic
Events easily retrieved from memory
must be highly probable.
Problem lies in factors that make events
stand in memory (e.g., distinctiveness,
emotional salience, frequency of
encoding/retrieval).
Simulation Heuristic
Construction of a mental model that
explains an event makes it seem
probable.
Hindsight bias—”I knew it all along.”