谁说说吉芬品和恶劣品的区别

吉芬品首先是一种劣等品,只不过比较特殊,收入效应大于替代效应.

吉芬品的替代效应与价格是反方向变动的，收入效应与价格同方向变动。

之所以出现价格下降而需求反而减少，是因为收入效应抵消了替代效应还有余。

我也想很好理解收入效应和替代效应。从图形上来看，一种这两个概念最本质的比较，最终是看无差异曲线的形状。是无差异曲线决定了收入效应和替代效应绝对值的大小！但是如何来确定该两种商品的无差异曲线，我就深入不下了。希望有高手能给出本质的回答！

In economics, a bad is the opposite of a good. "Bads" can helpfully be thought of as any goods with a negative value to the consumer, or a negative price in the marketplace. Garbage is an example of a bad.

A bad is a physical object that lowers a consumer's level of happiness, or stated alternately, a bad is an object whose consumption or presence lowers the utility of the consumer.

With normal goods, a two-party transaction results in the exchange of money for some object, e.g. money is exchanged for a car. With a bad (such as garbage), however, both money and the object in question go the same direction, e.g. a household loses money and the garbage. The waste collector is being compensated to take the object from the consumer. In this way, garbage has a negative price; the waste collector is receiving both garbage and money, and thus is paying a negative amount for the garbage.

Goodness and badness are an inherently subjective declaration, however. As an example: two diners at a restaurant discover that the "secret ingredient" in the house specialty is peanuts. One of the diners is a peanut-lover, and the other is allergic to peanuts. In this case, peanuts are, in the same time and in the same place, both a good and a bad in economic terms.

Additionally, one and the same good consumed by the same individual can turn into a bad over time, and vice versa; the nicotine from cigarettes may give a smoker a feeling of relieved anxiety and reduced stress. Continuing, long-term consumption of cigarettes, however, may have serious adverse effects on a smoker's health, thus turning the utility of cigarettes into the negative. On the other hand, some forms of medical treatment or side effects of medication may seem rather unpleasant to a patient at the time of treatment, but will greatly improve their health and well-being in the long run.

retrieved from http://en.wikipedia.org/wiki/Bad_(economics)

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GOODS AND BADS
There is a high degree of symmetry between economic goods and economic bads. Snow, litter and street mud are cited as examples. Economic growth obviously results in an increase in the supply of bads as well as goods. In addition, however, because it raises the value of time it can turn goods into bads and it can result in an end to the transformation of bads into goods. This is illustrated in some detail by two case studies for nineteenth century London, relating to domestic refuse and to horse manure. As a result of economic growth, horse manure had almost ceased to be an economic good and had become an economic bad by the end of the century.