亲爱的经济学家，

Dear Economist¹,

我与另一位母亲一起，给我5岁的孩子合办了一个生日聚会。我出了200英镑，但我收到了至少300英镑的礼物，我因此感到很内疚。作为一名客人，我不喜欢这些聚会，因为办聚会的人只出了一份食物，却收两份礼物。但合办聚会确实是一种理性的做法，因为你掏一半的钱，却收整份的礼，是这样吗？

I feel guilty because I paid ￡200 to co-host a birthday party for my five-year-old with another mother, but got at least ￡300 of gifts in return. As a guest, I don't like these parties because you take two gifts in return for only one party bag. But co-hosting is surely a rational thing because you pay half and get a full complement³ of presents?

一位来自南伦敦的母亲

South London Mum

亲爱的来自南伦敦的母亲，

Dear SLM,

祝贺你举办了效率更高的生日聚会。这似乎是一件趣事，因为你没有认识到这里面真正稀缺的资源。它不是聚会食物或者一次性玩具，而是时间。通过与一位朋友合办生日聚会，你为许多父母节省了时间，否则他们就需要连着参加两个这种聚会。孩子们可能会觉得受到了亏待，但过后可能就不会了。就算是5岁的孩子也不想天天聚会。

Congratulations on your move to more efficient birthday parties. It seems to be a happy accident, since you have failed to realise the true scarce resource here. It is not party bags or disposable toys, but time. By hosting a joint⁴ party with a friend, you are saving time for many parents who would have had to attend two such parties in quick succession. The children may feel hard done by but, then again, they may not. Even five-year-olds do not want a party every day.

至于通过这些聚会谋利，一位经济学家的理解是，礼物不需要立刻交换，价值也不需要严格对等。你举办了一个赚钱的聚会，但当其他人同样做时，你感觉受到了剥削——或许你应当将这些聚会看做是一个硬币的两面。这些利润和损失用不了多长时间就会扯平。信贷紧缩并不是那么严重，你不至于连一两个月都等不了，就盼着还礼吧？

As for making a profit on these parties, an economist understands that gifts need not be exchanged instantly and with exact accounting⁵ for value. You hosted a profitable party but feel exploited when others reciprocate⁶ – perhaps you should see these events as two sides of the same coin. It will not take long before these profits and losses even out. Surely the credit squeeze is not so severe that you cannot wait a month or two for a return on your gift giving?

至于聚会食物，它们当然是不道德的：为了减轻你的负罪感，你给其他人的孩子服用糖和添加剂。我建议你将聚会食物减半——我唯一的不满是，你没有将它们全部取消。

As for party bags, they are truly immoral⁷: to quell⁸ your feelings of guilt², you dose up other people's children with sugar and additives⁹. I commend your move to halve the supply of party bags – my only complaint is that you have not eliminated them altogether