Reasoning and Decision Making or The Shortcuts of the Human Mind (a.k.a Heuristics) by Elan Dubrofsky and Dina Tsirlin Reasoning • Cognitive processes by which people start with information and come to conclusions that go beyond that information Deductive Reasoning • Syllogism – Two statements called premises – Third statement called conclusion • Categorical Syllogism – Describe relation between two categories using all, no, or some Premise 1: All computer scientists are nerds. Premise 2: All nerds can name all six Star Wars movies. Conclusion: All computer scientists can name all six Star War movies. Deductive Reasoning • Syllogism is valid if conclusion follows logically from its two premises • Aristotle’s “perfect” syllogism – Premise 1: All A are B – Premise 2: All B are C – Conclusion: Therefore, All A are C Deductive Reasoning • If two premises of a valid syllogism are true, the syllogism’s conclusion must be true. – Do not confuse “validity” with “truth” The following syllogism is valid but not true All birds are animals All animals have four legs All birds have four legs How Well Can People Judge Validity? • Errors in evaluation – Atmosphere effect: use of words “all”, “some” or “no” in premises increase the probability of a conclusion with those words Belief bias: if syllogism is true or agrees with a person’s beliefs, more likely to be judged valid How do people go about determining whether a syllogism is valid/invalid? Mental Models of Deductive Reasoning • Specific situation that is represented in a person’s mind that can be used to help determine the validity of syllogisms • Iterative process Look for exceptions if no exception accept model and establish validity if exception modify the model until can be satisfied Deductive Reasoning • Conditional syllogisms – “If p, then q.” If I lend Emt $20, Then I won’t get it back. I lent Emt $20. Therefore, I won’t get my $20 back – Four types of conditional syllogisms • Affirming the antecedent • Denying the consequent • Affirming the consequent • Denying the antecedent The Wason Four-Card Problem • Effect of using real-world items in a conditional-reasoning problem – Determine minimum number of cards to turn over to test: If there is a vowel on one side, then there is an even number on the other side. Caption: The Wason four-card problem (Wason, 1966). • The Wason Four-Card Problem Falsification principle: to test a rule, you must look for situations that falsify the rule (exception) – Most participants fail to do this – When problem is stated in concrete everyday terms, correct responses greatly increase The Wason Four-Card Problem • Pragmatic reasoning schema: thinking about cause and effect in the world as part of experiencing everyday life – Permission schema: if A is satisfied, B can be carried out • Used in the concrete versions • People are familiar with rules Evolutionary Perspective on Cognition • Evolutionary principles of natural selection • Wason task governed by built-in cognitive program for detecting cheating Evolutionary Perspective on Cognition • Cosmides and Tooby (1992) – Created unfamiliar situations where cheating could occur – Participants did well – Evidence against permission schema Inductive Reasoning • Premises are based on observation and we generalize from these cases to more general conclusions with varying degrees of certainty Inductive Reasoning • Strength of argument – Representativeness of observations – Number of observations – Quality of observations ACTIVITY: Which argument is stronger? Why? 1. Observation: All sushi places I’ve seen in Vancouver charge a lot for sashimi. When I visited my family in Ottawa, the sashimi was expensive too. Conclusion: All sushi places charge a lot for sashimi. 2. Observation: Here in Ottawa, the sun has risen every morning. Conclusion: The sun is going to rise in Ottawa tomorrow. Inductive Reasoning • Used to make scientific discoveries – Hypotheses and general conclusions • Used in everyday life – Make a prediction about what will happen based on observation about what has happened in the past Heuristics • Availability heuristic: events more easily remembered are judged as being more probable than those less easily remembered • Is it easier to die for car accident of plane crash? Caption: Likely-causes-of-death experiment results. Pairs of “causes of death” are listed below the graph, with the least likely cause on the left. The number in parentheses on the right indicates how many more times more people were actually killed by the cause on the right. The bars in the graph indicate the number of people who judged the least likely alternative in each pair as causing the most deaths. (Adapted from Lichtenstein et al., 1978). Heuristics • Illusory correlations: correlation appears to exist, but either does not exist or is much weaker than assumed – Stereotypes A little experiment... Rate info: Among 100 people, 70 are lawyers, 30 are engineers A little experiment... Description: Jack, 45 yrs old, 4 kids, conservative, careful. Not interested in politics, many hobbies: math puzzles & carpentry – Lawyer or engineer? Heuristics • Representativeness Heuristic: the probability that A comes from B can be determined by how well A resembles properties of B – Use base rate information if it is all that is available – Use descriptive information if available and disregard base rate information Heuristics • Violation of Conjunction rule • Conjunction rule: probability of two events cannot be higher than the probability of the single constituents Caption: Because feminist bank tellers are a subset of bank tellers, it is always more likely that someone is a bank teller than a feminist bank teller. Heuristics • The Confirmation Bias: tendency to selectively look for information that conforms to our hypothesis and overlook information that argues against it Heuristics • The Confirmation Bias • Lord and coworkers (1979) – Had those in favor of capital punishment and those against capital punishment read the same article • Those in favor found the article in favor • Those against found the article against Decision Making • Economic utility theory – People are rational and if they have all relevant information they will make a decision which results in the maximum expected utility Decision Making • Utility: outcomes that are desirable because they are in the person’s best interest – Maximum monetary payoff Decision Making • Problems for Utility Approach – Not necessarily money, people find value in other things – Many decisions involve payoffs that cannot be calculated “Good enough” philosophy (Herb Simon, Psychologist Nobel Prize!!!) Caption: Behavioral results of Sanfey and coworkers’ (2003) experiment, showing responders’ acceptance rates in response to different offers made by human partners and computer partners. Decision Making • Focusing illusion: focus on just one aspect of situation and ignore other aspects that may be important – Dating and happiness – California versus Midwest living • Decision Making Decisions depend on how choices are presented – Opt-in procedure • active step to be organ donor – Opt-out procedure • Organ donor unless request not to be Subject’s consent to research participation Active Consent Passive consent Decision Making • Risky decisions – Risk-aversion strategy used when problem is stated in terms of gains – Risk-taking strategy when problem is stated in terms of losses Decision Making • Framing effect: decisions are influenced by how a decisions is stated – Can highlight one aspect of situation Decision Making • Decision-making process includes looking for justification so a rationale presented with decision • Decision Making Tversky and Shafir (1992) – “pass” - go on trip – “fail” - do not – “I don’t know yet” – wait to find out results before making decision to go on trip or not In Conclusion... • • We're only human... therefore our thinking is very flawed. Be careful to make sure that when you use a heuristic, it's not leading you down a dangerous path.