Inferior goods - Letto Uzai (English spelling)

Japanese: 劣等財 - れっとうざい（英語表記）inferior goods

When the demand for a good decreases as income increases, that is, when the demand changes in the opposite direction to the change in income, the good is called an inferior good. On the other hand, if the demand changes in the same direction, the good is called a normal good. There are exceptional cases where the law of demand, which states that a fall in price increases the demand for the good, does not hold true. This is when the good is an inferior good and its income effect exceeds its substitution effect. In this case, the good is called a Giffen good. A consumer who prefers butter to margarine will refrain from purchasing margarine as his or her income level rises, and will use that money to purchase butter.

Source: Heibonsha World Encyclopedia, 2nd Edition Information

Japanese:

ある財が所得の増加に対し需要が減少する，すなわち需要の変化が所得の変化と逆方向であるとき，その財を劣等財または下級財という。他方，同方向であれば，正常財または普通財という。〈価格下落がその財の需要を増加させる〉という需要法則が例外的に成立しない場合がある。それは，財が劣等財で，かつその所得効果が代替効果を上まわる場合であり，このときとくにギッフェン財Giffen goodsと呼ぶ。マーガリンよりバターを好む消費者は，所得水準が上がるにしたがって，マーガリンの購入をひかえ，その分をバターの購入に当てるであろう。

出典　株式会社平凡社世界大百科事典第２版について　情報

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