The "ultimatum game" is an economics experiment developed in 1982 that uses two participants and a fixed amount of money. One participant is designated the "offerer" and the other is designated the "decider." The offerer proposes a way of splitting the money with the decider. If the decider accepts the offer, the two participants share the money as proposed. But if the decider determines that the proposed split is unfair, he or she can reject the offer, and both participants get nothing.

The ultimatum game reveals that people's sense of fairness can overwhelm their desire for free money. For instance, if the offerer proposes a split of $9 to the offerer and $1 to the decider, the decider will usually punish the offerer by rejecting the offer. That means the offerer won't get the $9, but it also means the decider won't get $1 he or she could have gotten for doing nothing. Another interesting observation is that women deciders, on average, are more willing to take a lower offer than men deciders, and offerers are more likely to make lower offers to woman deciders than men deciders.

On his Priceless blog, author William Poundstone shows how these gender-based economics are used against women in the supermarket. Manufacturers take advantage of the fact that women aren't as "price-sensitive" as men and charge more for products packaged for women than identical products packaged for men. The January 2010 issue of Consumer Reports looked into this practice and asked manufacturers to explain themselves. The answers are amusing -- shaving cream for women costs more because women shave in the shower and so the product has to be packaged in rust-proof cans, and body wash for women "has skin-sensation technology."

What can be done about this? Sure, people could complain to manufacturers, but as Poundstone points out, Consumer Reports' practical advice is probably the most effective way to save money and get manufacturers to change their behavior: "Ignore the gender marketing and buy whatever is cheaper."

Mark Frauenfelder – Editor-in-chief of MAKE magazine and the founder of the popular Boing Boing weblog, Mark was an editor at Wired from 1993-1998 and is the founding editor of Wired Online.