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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
conclusio n s are su g g e s ted, d e cide h ow str o n g arg u ment is.
Us e p a s t ex p eri enc e s to g uide pre s e nt b ehavio ur (sh or t cuts), which take the form of h euristic s.
Heuristics – “rule of th u mb” that are likely to provide the corr e c t answer to a pro blem. NOT FOOLPROOF.
state s that events that are more e a sily remembered are ju d g ed a s b eing more pro b able than events that a
oExample: which is more prevalent – words b egin nin g wit h r, or words wit h r a s third lett er? (l att er)
oExample: which are the more com m on c a us e s of d e a th in the US
Explanation of m isju d g ements linked to avail ability.
oMcKelvie : pre s e nted list of 2 6 n ame s to p ar ticipants.
Co n ditio n s:
•“famous men” – 1 2 famous men , 1 4 n o n famous women
•“famous women” – 1 2 famous women , 1 4 n o n famo u s men
par ti cipants a sked to e s ti m ate whether there were more male s or female s
answer d epen d ed to which co n dition they were ex p o s e d to.
This wa s b e c a us e famo u s n ame s e a sier to remember, stands out more. (availability)
Illusory corr elatio n s : o c c ur when a cor r elation b/w 2 events ap p e a r to exist b u t there is n o n e/we a k.
oE.g. stereoty p e s .
related to ide a that p eo ple make ju d g ments b a s e d o n h ow o n e event re s e mble s an o ther.
Prob ability that A is a member of cla s s B c a n b e d etermi ned by h ow well p ro p er ti e s of A re s e mble B.
Tversky an d Kahn eman :
oExp eri ment 1: Rob er t we a rs gla s s e s , spe a ks quietly an d re a ds a lot. Is it more likely h e is a librari an
most answered librari an (ignoring the p o p ulation b a s e rate – more likely h e wa s farmer)
oExp eri ment 2: Lind a is 3 1, sin gle, o u tspoken an d brig h t. Majored in philosop h y, d e e ply co n c erned w
discri mi nation an d social justic e an d p ar ticipated in anti n u cle ar d emonstr atio n s.
Lind a is a b an k teller. // Lind a is a b ank tell er an d is a c tive in the femi nist mo v ement.
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