Bloomberg’s proposal makes clever use of what economists call “default bias.” If you offer a choice in which one option is seen as a default, most people go for that default option. People who are automatically enrolled in a retirement plan, for instance, are more likely to stay with their original plan than those who choose plans for themselves. In countries where people have to choose to be an organ donor, most people aren’t donors; in countries where people have to actively say they don’t want to be an organ donor, most are donors. The soda ban makes sixteen ounces or less the default option for soda drinkers; if they want more, they’ll have to make an extra effort.
(via The Economics of Michael Bloomberg’s Large-Soda Ban : The New Yorker)