1.2.4.7 Applications of indifference curve analysis: substitution effect and income effect for a normal good, inferior good and a giffen good; derivation of the Engels curve

Indifference curve analysis is a powerful tool in economics that finds applications in various scenarios. Two significant applications of indifference curve analysis are the substitution effect and the income effect, which help in understanding consumer behavior in response to changes in prices and income.

1. Substitution Effect and Income Effect:

a. Substitution Effect: The substitution effect measures the change in the quantity demanded of a good due to a change in its relative price, while keeping the consumer’s satisfaction (utility) constant. When the price of a good changes, consumers may substitute it for a relatively cheaper or more affordable alternative to maintain their level of utility.

• Normal Good: For a normal good, as the price of the good decreases, the substitution effect leads to an increase in its quantity demanded. Consumers switch from relatively more expensive goods to the now relatively cheaper good.
• Inferior Good: For an inferior good, as the price of the good decreases, the substitution effect leads to a decrease in its quantity demanded. Consumers now prefer relatively more expensive goods to the inferior good, which they perceive as less desirable.

b. Income Effect: The income effect measures the change in the quantity demanded of a good due to a change in the consumer’s real income, while keeping the relative prices constant. When the consumer’s income changes, their purchasing power alters, impacting their demand for goods.

• Normal Good: For a normal good, as the consumer’s income increases, the income effect leads to an increase in its quantity demanded. Consumers can now afford to buy more of the good at each price level.
• Inferior Good: For an inferior good, as the consumer’s income increases, the income effect leads to a decrease in its quantity demanded. Consumers now have a higher income and can afford relatively more expensive goods, reducing their demand for the inferior good.
• Giffen Good: A Giffen good is a rare case where the income effect outweighs the substitution effect. For a Giffen good, as the price of the good increases, the income effect leads to an increase in its quantity demanded. This occurs when the Giffen good is considered a staple or necessity, and the income effect dominates the substitution effect.

2. Engels Curve: The Engels curve is an application of indifference curve analysis that shows the relationship between the quantity demanded of a good and the consumer’s income, while keeping the prices of goods constant. The Engels curve provides insights into how the demand for a specific good changes as income changes.

• For a normal good, the Engels curve typically slopes upwards, indicating a positive relationship between income and the quantity demanded of the good. As income increases, consumers demand more of the normal good.
• For an inferior good, the Engels curve typically slopes downwards, indicating a negative relationship between income and the quantity demanded of the good. As income increases, consumers demand less of the inferior good and switch to relatively more expensive alternatives.