CMU professor Loewenstein and associates conducted an experiment in which they offered first-year business-school students at Sloan the opportunity to buy a range of luxury goods, including an "average" and a "rare" bottle of French wine, without referring to the actual price of the goods.

The catch was that subjects had to first state whether they would buy the bottles of wine at a price determined arbitrarily by the last two digits of their Social Security numbers (that is, 34 becomes $34). The students were then asked the maximum price they would pay for the bottles.

The Social Security number game is a trick called "anchoring manipulation" that's borrowed from experimental psychology, and for some reason it makes otherwise rational people do irrational things.

For no logical reason, students with Social Security digits higher than 50 said they would pay nearly twice as much as those with digits less than 50, even when reminded that this pricing system was completely arbitrary.

http://www.salon.com/mwt/style/2002/03/11/silly_spending/print.html