楼上：任何一种现象都有其原因，特例也不例外。

inferior Goods是什么意思?为啥积分土豆是inferior Goods?

inferior Goods是劣等品的意思，劣等品的收入效应为负，如上面条件中的爱尔兰土豆，如果消费者的货币收入提高了，就会减少对于它的需求，反之则增加它的需求。从Slutsky Equation来看，一种商品需求量与其价格反方向变动的必要条件是收入效应为负。

土豆有营养啊！哈哈！

哥们可不能这么说话，任何的经济学问题的提出有其合理的成分，更有其局限性。吉分可能正是忽略了当时的某些限制或关系，而错误的提出了这一个观点。对于吉分商品，我和楼主一样，也是时时持有怀疑，总觉得是否忽略了土豆的替代产品价格的变化。而且，对于吉分商品的描述是需求随着价格的升高而增长，真的是价格引起了需求还是需求进一步带动了价值？

土豆之所以是劣等品是相对于肉类来说。爱尔兰的主食应该是土豆、牛肉和鸡肉之类的。每单位货币的土豆的热量高于肉类，但其美味却不如肉类。从美味的角度当时的人们愿意更多地食用肉类，所以土豆被认为是劣等品。其实这是个不确切的说法。

当时的优质食品价格张了多少?

a major problem with this explanation is that it disregards Marshall'observation that both supply and demand fators must be taken into account when analyzing price changes.

if potatoes increased because of the potato blight in Ireland ,then supply should have become small, so how could more potatoes possibly have been consumed? Also, since many Irish people were potato farmers,the potatoes price increase should have increased real income for them.

土豆有极高的营养价值啊。

这个问题与优质食品涨价无关，也就是说无论肉类是否涨价，单位货币购买肉类所购得的热量一定小于购买土豆所得的热量。当一个人吃不饱时，其关心的首要问题是如何让自己吃饱。

土豆不仅是吉芬品，还是必需品，所以，由于土豆价格的上升，为了能维持生命，就必须减少其他食品的消费，毕竟，相对于其他商品来讲，土豆还是最便宜的，所以才会出现价格上升而消费量上升的现象。

第二，吉芬品质是一定时间内的吉芬品，随着收入的增加，原先的吉芬品也会变成正常品。这和收入的多少有关。

如果发现有一个爱尔兰饥民只吃土豆（这里的土豆看作是Giffen Goods，因而是inferior Goods，在他的效用函数中只有土豆唯一变量，那么这个饥民的行为还是追求效用最大化吗？如果是的话，这不就与消费商品不可能都是inferior Goods相悖了吗？

回楼上：

如果我们没有发现那样的爱尔兰饥民呢？

建议看看斑竹有关吉芬商品的讨论帖。

[此贴子已经被作者于2006-10-24 1:26:51编辑过]

18楼的,如果一个爱尔兰人只吃土豆,那么就不存在吉芬品的问题了,那对于他来讲,不存在选择问题,土豆对于他来讲,是一种完全不弹性商品,所以,也就不是吉芬品了.

着么看,土豆是吉芬品,就必须是inferior Goods,并且可以被高级的替代,如果以上的成立,饥民就该另有更好的替代物,看起来当时更多物品是有,但因饥民为支付能力,等于没有,即使土豆飞张,估计价格可能没超过同期的高级替代品,饥民从支付上没有更多可选择,这样,土豆对饥民来说不是吉芬品,对有更好支付能力的是,如果说土豆是积分品,或者要先设定正常的购买能力高于土豆,并且表达达方必须有此支付能力,所以饥民没条件说土豆是吉芬品,只要不是当时的饥民,都可以说在当时正常支付情况下,土豆是吉芬品

应该说土豆因为是必需品才可能是吉芬品，这当中是有因果关系的。

words about this problem from Microeconomics and Behavior by Robert H.Frand:
Modern historians dispute whether the potato ever was really a Giffen food. Whatever the resolution of this dispute, the potato story does illustrate the characteristics that a Giffen good would logically have to possess. First, it would not only have to be inferior, but also have to occupy a large share of the consumer's budget. Otherwise, an increase in tits price would not create a significant reduction in real purchasing power. (Doubleing the price of keyrings,for example, does not amke anyone appreciably poorer.) The second characteristic required of a Giffen good is that it have a relatively small substitution effect, one small enough to be overwhelmed by the income effect.
In practice, it is extremely unlikely that a good will satisfy both properties required of a Giffen good. Most goods, after all, account for only a tiny share of the consumer's total expenditures. Moreover, as noted, the more broadly a good is defined, the less likely it is to be inferior. Finanlly, inferior goods by their very nature tend to be substitute ground sirloin for hamburge, for example, is precisely what makes hamburger tend to be an inferior good.
The Giffen good is an intriguing anomaly, chiefly useful for testing students' understanding of the subtleties of income and substitution effects....

[此贴子已经被作者于2006-10-26 17:52:32编辑过]

土豆？？？？？？？？？？

貌似吉芬物品是非常特殊的,生活中很少,不好研究啊