In economics, money illusion, or price illusion, is a cognitive bias where money is thought of in nominal, rather than real terms. In other words, the face value (nominal value) of money is mistaken for its purchasing power (real value) at a previous point in time. Viewing purchasing power as measured by the nominal value is false, as modern fiat currencies have no intrinsic value and their real value depends purely on the price level. The term was coined by Irving Fisher in Stabilizing the Dollar.
Money illusion
Wikipedia
https://en.wikipedia.org/wiki/Money_illusion
In economics, money illusion, or price illusion, is a cognitive bias where money is thought of in nominal, rather than real terms. In other words, the face value (nominal value) of money is mistaken for its purchasing power (real value) at a previous point in time. Viewing purchasing power as measured by the nominal value is false, as modern fiat currencies have no intrinsic value and their real value depends purely on the price level. The term was coined by Irving Fisher in Stabilizing the Dollar. It was popularized by John Maynard Keynes in the early twentieth century, and Irving Fisher wrote an important book on the subject, The Money Illusion, in 1928.
The existence of money illusion is disputed by monetary economists who contend that people act rationally (i.e. think in real prices) with regard to their wealth. Eldar Shafir, Peter A. Diamond, and Amos Tversky (1997) have provided empirical evidence for the existence of the effect and it has been shown to affect behaviour in a variety of experimental and real-world situations.
Shafir et al. also state that money illusion influences economic behaviour in three main ways:
Price stickiness. Money illusion has been proposed as one reason why nominal prices are slow to change even where inflation has caused real prices to fall or costs to rise.
Contracts and laws are not indexed to inflation as frequently as one would rationally expect.
Social discourse, in formal media and more generally, reflects some confusion about real and nominal value.
Money illusion can also influence people’s perceptions of outcomes. Experiments have shown that people generally perceive an approximate 2% cut in nominal income with no change in monetary value as unfair, but see a 2% rise in nominal income where there is 4% inflation as fair, despite them being almost rational equivalents. This result is consistent with the ‘Myopic Loss Aversion theory’. Furthermore, the money illusion means nominal changes in price can influence demand even if real prices have remained constant.
Explanations and implications
Explanations of money illusion generally describe the phenomenon in terms of heuristics. Nominal prices provide a convenient rule of thumb for determining value and real prices are only calculated if they seem highly salient (e.g. in periods of hyperinflation or in long term contracts).
Some have suggested that money illusion implies that the negative relationship between inflation and unemployment described by the Phillips curve might hold, contrary to more recent macroeconomic theories such as the “expectations-augmented Phillips curve”. If workers use their nominal wage as a reference point when evaluating wage offers, firms can keep real wages relatively lower in a period of high inflation as workers accept the seemingly high nominal wage increase. These lower real wages would allow firms to hire more workers in periods of high inflation.
Money illusion is believed to be instrumental in the Friedmanian version of the Phillips curve. Actually, money illusion is not enough to explain the mechanism underlying this Phillips curve. It requires two additional assumptions. First, prices respond differently to modified demand conditions: an increased aggregate demand exerts its influence on commodity prices sooner than it does on labour market prices. Therefore, the drop in unemployment is, after all, the result of decreasing real wages and an accurate judgement of the situation by employees is the only reason for the return to an initial (natural) rate of unemployment (i.e. the end of the money illusion, when they finally recognize the actual dynamics of prices and wages). The other (arbitrary) assumption refers to a special informational asymmetry: whatever employees are unaware of in connection with the changes in (real and nominal) wages and prices can be clearly observed by employers. The new classical version of the Phillips curve was aimed at removing the puzzling additional presumptions, but its mechanism still requires money illusion.
貨幣錯覚
ウィキペディア
https://ja.wikipedia.org/wiki/貨幣錯覚
貨幣錯覚（money illusion）とは、人々が実質値ではなく名目値に基いて物事を判断してしまうこと。本来、貨幣価値の変化を考慮した購買力によって判断しなければならない時に、金額を通じて判断を行なってしまうこと。貨幣の中立性が成立しなくなる一要因である。
貨幣はそれ自身が何か有用であるわけではなく、あくまで貨幣によって購入されたものから満足を得ることができる。つまり、名目的な貨幣額ではなく実質的な購買力こそが重要なはずである。それにもかかわらず、人々には名目の貨幣額に基づいて行動を決定する傾向があり、それをアーヴィング・フィッシャーは貨幣錯覚と名付けた。その後、多くの実証分析や実験などによって、存在が確認されてきた。
たとえば、10%のインフレーションが起きることを知っている企業が名目賃金を5%引き上げたとする。このとき実質賃金は低下しているが、労働者が名目賃金の上昇だけを見て労働供給を増やそうとするような場合、労働者は貨幣錯覚に陥っていると言う。
あるいは、1%のデフレ経済において、手取りの給料が500万円から499万円に下がったとする。このとき実質の給料は増えており購買力は上昇しているにもかかわらず、名目の給料が減っていることを見て支出を減らそうとするような場合にも、貨幣錯覚が起きている。
また、2%のインフレ下において名目賃金を1%引き上げることと、1%のデフレ下において名目賃金を2%引き下げることは、実質で見るとほぼ同じことである。しかし労働者が、名目賃金が減ってしまう後者に対して、前者に対するよりも非常に強く反対するということが見られる。これも貨幣錯覚の一つである。
なお、貨幣「錯覚」とは呼ばれるものの、これは非合理的行動であるとは限らない。実質化して購買力に基いて考えるには、今後それぞれが購入する可能性のある様々な財の将来の物価に関する知識が必要となるが、それを正確に知ることはできないため、より不確実性の低い名目値をベースに考えることには合理性がある。また、契約や法のように名目値で固定され、実質化して考えることが適さない事象も多いため、やはり名目値を基準に判断することには一定の合理性がある。たとえば、持ち家の購入など、ある時点で将来までの消費を約束するような契約によって、理論的にも人々が名目値を重視する可能性が高くなることが指摘されている。