Reasoning and Judgment PSY 421 – Fall 2004

Overview Reasoning Judgment Heuristics Other Bias Effects

Reasoning Deductive – drawing a conclusion based on general principles or assertions (reasoning from general to specific) –Syllogistic Reasoning – determining whether a conclusion is valid given the truth of the two quantified premises (all, some, none) Some A is B. All B is C. Therefore, some A is C. –Errors in syllogistic reasoning All A are B. All C are B. Therefore, all A are C. Atmosphere effects – context of the syllogism affects perceived validity Belief Bias – assessing truth of the premises based on biased beliefs –All smart people are reasonable –All Democrats are smart people –Therefore, all Democrats are reasonable –Conditional Reasoning – if/then statements (If P, then Q) – watch out for biconditionality

Reasoning, continued Inductive Reasoning – reasoning from specific to general –Generalizations Observation: John came to class late this morning. Observation: John’s hair was uncombed. Prior experience: John is very fussy about his hair. Conclusion: John overslept –Evaluated on strength rather than validity (how solid is the conclusion based on the evidence)

Judgment Extension of inductive reasoning Human ability to infer, estimate, and predict the character of unknown events (Hastie & Dawes, 2001) A great deal of research exists on how people judge one another (social psychology) –Stereotyping –Discrimination –Heuristics

Heuristics Chapter 12 – Problem Solving – heuristics are general strategies Availability heuristic – base estimates of likelihood (probability) on the ease with which we can think of examples – ease of remembering issue –Biased encoding – what do we hear more about? Death by flood or death from asthma –Biased retrieval – sampling memory and recency Representativeness Heuristic – assessing the degree to which a object represents our basic idea of that object; something has characteristics of a certain class (e.g., stereotype) –Base Rates –Conjunction Fallacy –Event Clusters Hot Hand Gambler’s Fallacy

Other Bias Effects Anchoring and Adjustment – overly biased toward a first impression; initial piece of information –The Spotlight Effect – tendency to believe that our actions and appearance are noticed by others more than they actually are Hindsight Bias – I knew it all along effect Miscalibration of Confidence – over or under confidence regarding judgments or decisions