The babysitting co-op Krugman referred to was a barter market where people can only trade ONE thing.
And where each member had to contribute 14 hours worth of babysitting a year just to pay for using the system. That's why there was more supply than demand in that "market" when it started.
And where each member had to contribute 14 hours worth of babysitting a year just to pay for using the system. That's why there was more supply than demand in that "market" when it started.