Saturday, 18 April 2009

Irrationality, salad and chips - failure of the independence axiom

One of the basic tenets of our approach in economics is that the mere presence of an extra possible choice in the options available to a rational consumer should not affect the decision taken, as long as the consumer does not choose the extra choice itself. This is a version of the "independence of irrelevant alternatives" assumption that crops up in pretty much all rationalchoice theories. However, it seems that the mere presence of a salad on a menu, even if not chosen, makes diners more likely to opt for chips. See this article.
"Investigators asked college students to choose foods from menus that differed in only one feature; one menu offered a salad and the other did not. The point? To find out whether the presence of a salad on the menu influenced what else the students ate. It did. The students choose French fries more often from the menu with the salad."

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