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ut given the choice of a $50 sure gain or a 50% chance of gaining $100,we take the sure thing. This is shown in the hypothetical value functiondepicted in Figure 13.2. They also found that people weigh events withlow probability more heavily than events with moderate or high probability,relative to their expected outcomes. One result of this is that problemscan be framed so that people are likely to choose a dominatedalternative—a clearly inferior choice, which is to say one that is worsethan other options in some situations and better in none. 19Preferences are heavily influenced by how a choice is framed: peopleprefer a surgery that offers an 80% survival rate to one that offers a 20%mortality rate. 20 Preferences are heavily influenced by default choices.There is an enormous disparity across countries in the number of peoplewho agree to donate their organs to others in the event of death, a decisionpeople are typically asked to make when they get a driver’s license. Itturns out that disparity is explained almost entirely by whether checkinga box opts you in to donating organs or opts you out. In European countries,where one has to opt in to donating organs, donation rates rangefrom 4.25% to 27.5%, while in countries where one has to opt out, ratesrange from 86% to 100%. 21 Similarly, if people have to opt in to retirementsavings, they are much less likely to save than if they have to opt out.Preferences are heavily influenced by whether we think about the benefitsof policy first or the costs (we’re more likely to favor a policy if we thinkabout benefits first) and if we make decisions on our own or in a group(being in a group may lead us to give more weight to the future, for example).22Chapter 13 Human Behavior and Economics • 243■ Self-InterestWhen choosing between different options that affect only their personalwell-being, nonrational behavior can lead people to make the wrongchoice. When choosing between options that benefit either the individualor society, both nonrational and selfish behavior can undermine socialwell-being. Most of us know from simple introspection that we are notpurely self-interested, and we constantly hear of people making significantsacrifices for others. At the same time, however, evidence of purely selfish19 A. Tversky and D. Kahneman, The Framing of Decisions and the Psychology of Choice, Science211:453–458 (1981). We refer you to this article for examples of dominated alternatives.20 C. Sunstein and R. Thaler, Libertarian Paternalism Is Not an Oxymoron, University of ChicagoLaw Review 70:1159–1202 (2003).21 E. Johnson and D. Goldstein, Medicine: Do Defaults Save Lives? Science 302:1338–1339(2003).22 J. Gertner, Why Isn’t the Brain Green? New York Times Magazine, April 16, 2009.