Adults In a 1972 experiment, participants were divided into two groups, with the former being told they would receive a mild electric shock and the latter told that there was a 50 percent chance they would receive such a shock. When the subjects' physical anxiety was measured, there was no difference between the two groups. This lack of difference remained even when the second group's chance of being shocked was lowered to 20 percent, then ten, then five. The conclusion: "we respond to the expected magnitude of an event...but not to its likelihood. In other words: We lack an intuitive grasp of probability." Baron (2000) suggests that the bias manifests itself among adults especially when it comes to difficult choices, such as medical decisions. This bias could make actors drastically violate expected-utility theory in their decision making, especially when a decision must be made in which one possible outcome has a much lower or higher utility but a small probability of occurring (e.g. in medical or gambling situations). In this aspect, the neglect of probability bias is similar to the
neglect of prior base rates effect. Cass Sunstein has cited the history of
Love Canal in upstate
New York, which became world-famous in the late 1970s owing to widely publicized public concerns about abandoned waste that was supposedly causing medical problems in the area. In response to these concerns, the
U.S. federal government set in motion "an aggressive program for cleaning up abandoned
hazardous waste sites, without examining the probability that illness would actually occur," and legislation was passed that did not reflect serious study of the actual degree of danger. Furthermore, when controlled studies were publicized showing little evidence that the waste represented a menace to public health, the anxiety of local residents did not diminish. One
University of Chicago study showed that people are as afraid of a 1% chance as of a 99% chance of contamination by poisonous chemicals. In 2016,
Rolf Dobelli presented a choice between two
games of chance. In one, you have a one in 100 million chance of winning $10 million; in the other, you have a one in 10,000 chance of winning $10,000. It is more reasonable to choose the second game; but most people would choose the first. For this reason, jackpots in lotteries are growing.
Children The probability bias is especially pronounced among children. In a 1993 study, Baron, Granato, Spranca, and Teubal presented children with the following situation: ''Susan and Jennifer are arguing about whether they should wear seat belts when they ride in a car. Susan says that you should. Jennifer says you shouldn't... Jennifer says that she heard of an accident where a car fell into a lake and a woman was kept from getting out in time because of wearing her seat belt, and another accident where a seat belt kept someone from getting out of the car in time when there was a fire. What do you think about this?''
Jonathan Baron (2000) notes that subject X responded in the following manner: :A: Well, in that case I don't think you should wear a
seat belt. :Q (interviewer): How do you know when that's gonna happen? :A: Like, just hope it doesn't! :Q: So, should you or shouldn't you wear seat belts? :A: Well, tell-you-the-truth we should wear seat belts. :Q: How come? :A: Just in case of an accident. You won't get hurt as much as you will if you didn't wear a seat belt. :Q: OK, well what about these kinds of things, when people get trapped? :A: I don't think you should, in that case. It is clear that subject X completely disregards the probability of an accident happening versus the probability of getting hurt by the seat belt in making the decision. A normative model for this decision would advise the use of
expected-utility theory to decide which option would likely maximize utility. This would involve weighing the changes in utility in each option by the probability that each option will occur, something that subject X ignores. Another subject responded to the same question: :A: If you have a long trip, you wear seat belts half way. :Q: Which is more likely? :A: That you'll go flyin' through the windshield. :Q: Doesn't that mean you should wear them all the time? :A: No, it doesn't mean that. :Q: How do you know if you're gonna have one kind of accident or the other? :A: You don't know. You just hope and pray that you don't. Again, the subject disregards the probability in making the decision by treating each possible outcome as equal in his reasoning. ==Practical consequences==