6.2 Thinking Under Uncertainty

person-who reasoning

Questioning a well-established research finding because one knows a person who violates the finding. i.e. questioning the validity of the finding that smoking leads to health problems, because we know someone who has smoked most of his or her life and has no health problems

heuristic

(words that are more available in our memory are more probable) to answer the probability question

availability heuristic

the rule of thumb that the more available an event is in our memory, the more probable it is

*The Overlapping Set Diagram for the Linda Problem*

The overlap (the green area) of the two sets (all bank tellers and all people active in the feminist movement) indicates the probability of being both a bank teller and active in the feminist movement. Because this area is a subset (part) of each of the two sets, its probability has to be less than that for either of the two sets. This is the conjunction rule.

belief perseverance

The tendency to cling to one's beliefs in the face of contradictory evidence.

confirmation bias

The tendency to seek evidence that confirms one's beliefs. ie. the number sequence "2-4-6" task

representativeness heuristic

A heuristic for judging the probability of membership in a category by how well an object resembles (is representative of) that category (the more representative, the more probable). Simply put, the rule is: the more representative, the more probable.

dread risk

Availability in memory also plays a key role in what is termed a dread risk. A dread risk is a low-probability, high-damage event in which many people are killed at one point in time. Not only is there direct damage in the event, but there is secondary, indirect damage mediated through how we psychologically react to the event. A good example is our reaction to the September 11, 2001, terrorist attacks (Gigerenzer, 2004, 2006). Fearing dying in a terrorist airplane crash because the September 11 events were so prominent in our memories, we reduced our air travel and increased our automobile travel, leading to a significantly greater number of fatal traffic accidents than usual.

gambler's fallacy

Incorrectly believing that a chance process is self-correcting in that an event that has not occurred for a while is more likely to occur. i.e. Suppose a person has flipped eight heads in a row and we want to bet $100 on the next coin toss, heads or tails. Some people will want to bet on tails because they think it more likely, but in actuality the two events are still equally likely

conjunction fallacy

Incorrectly judging the overlap of two uncertain events to be more probable than either of the two events. i.e. Linda is a bank teller and active in the feminist movement illustrates the conjunction fallacy

*Wason's demonstrations* the number sequence "2-4-6"

Most of the participants do not name the correct rule. They devise a hypothesis (e.g., "numbers increasing by 2") and proceed to test the hypothesis by generating series that conform to it (e.g., 8-10-12). In other words, they test their hypotheses by trying to confirm them. Did you do this? People do not test their hypotheses by trying to disconfirm them (e.g., generating the sequence 10-11-12 for the hypothesis "numbers increasing by 2"). The tendency to seek evidence that confirms one's beliefs is called confirmation bias. This bias is pervasive in our everyday hypothesis testing, so it is not surprising that it occurs on the 2-4-6 task. The 2-4-6 task serves to highlight the inadequacy of the confirmation bias as a way to test a hypothesis. The experimenter's rule for the 2-4-6 task was a very simple, general rule, so most sequences that people generated conformed to it. What was it? The rule was simply any three increasing numbers; how far apart the numbers were did not matter. *To truly test a hypothesis, we must try to disconfirm it*

Why do people commit the gambler's fallacy? Again, they are using the representativeness heuristic (Tversky & Kahneman, 1971). People believe that short sequences (the series of eight coin tosses or the 26 spins of the roulette wheel) should reflect the long-run probabilities.

Simply put, people believe random sequences, whether short or long, should look random. This is not the case. Probability and the law of averages only hold in the long run, not the short run.

Physicians (and patients) also seem to have difficulty in interpreting positive test results for medical screening tests, such as for various types of cancer and HIV/AIDS (Gigerenzer, 2002). They often overestimate the probability that a patient has a disease based on a positive test result

When considering what a positive result for a screening test means, you are testing the hypothesis that a patient actually has the disease being screened for by determining the probability that the patient has the disease given a positive test result.

illusory correlation

the erroneous belief that two variables are statistically related when they actually are not. If we believe a relationship exists between two things, then we will tend to notice and remember instances that confirm this relationship. i.e. people erroneously believe that a relationship exists between weather changes and arthritis.

*Wason's demonstrations* four-card selection task

you should decide what type of card would falsify the rule. The rule states that if a card has a vowel on one side, it has to have an even number on the other side. Therefore, a card with a vowel on one side and an odd number on the other side would falsify the rule. So why do people select the cards showing A and 4? As in the 2-4-6 task, people focus on confirmation and select cards to verify the rule (show that it is true). Instead of deducing what will falsify (disconfirm) the rule, people merely try to confirm it (demonstrating confirmation bias).