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PSY270 Lecture 11
Reasoning and Decision Making
Decisions: making choices between alternatives
Reasoning: process of drawing conclusions, and as the cognitive processes by which people start with
information and come to conclusions that go beyond that information
oDeductive: involves sequences of statements called syllogisms. E.g. “All robins are birds.”
oInductive: arrive at conclusions about what is probably true based on evidence.
Conditional reasoning: the Wason four-card problem (COGLAB)
Classic reasoning problem
o4 cards shown, e.g. E K 4 7
oEach card has letter on one side and a number on the other side.
oTask is to indicate which cards you need to turn over to test this rule:
If there is a vowel on one side, then there is an even number on the other side.
o53% of participants indicated E must be turned over. (correct, falsify rule)
o46% indicated that 4 would be needed (in addition to E). (incorrect, tells us nothing about rule)
o4% got correct answer – 7.
Key: falsification principle – to test a rule, it is necessary to look for situations that would falsify the rule.
Inductive reasoning: reaching conclusions from evidence
premises based on observation generalization
Nature of inductive reasoning
conclusions are suggested, decide how strong argument is.
Use past experiences to guide present behaviour (shortcuts), which take the form of heuristics.
Heuristics – “rule of thumb” that are likely to provide the correct answer to a problem. NOT
states that events that are more easily remembered are judged as being more probable than events that
are less easily remembered.
oExample: which is more prevalent – words beginning with r, or words with r as third letter?
oExample: which are the more common causes of death in the US
Explanation of misjudgements linked to availability.
oMcKelvie : presented list of 26 names to participants.
•“famous men” – 12 famous men, 14 non famous women
•“famous women” – 12 famous women, 14 non famous men
participants asked to estimate whether there were more males or females
answer depended to which condition they were exposed to.
This was because famous names easier to remember, stands out more. (availability)
Illusory correlations : occur when a correlation b/w 2 events appear to exist but there is none/weak.
related to idea that people make judgments based on how one event resembles another.
Probability that A is a member of class B can be determined by how well properties of A resemble B.
Tversky and Kahneman :
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