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Indifference curve
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Indifference curve

In microeconomics, an indifference curve is a graph showing combinations of two goods to which an economic agent (such as a consumer or firm) is indifferent, that is, it has no preference for one combination over the other. They are used to analyse the choices of economic agents.

For example, if a consumer was equally satisfied with 1 apple and 4 bananas, 2 apples and 2 bananas, or 5 apples and 1 banana, these combinations would all lie on the same indifference curve.

For a given pair of goods, many indifference curves can be drawn. The consumer is generally assumed to prefer combinations of goods representing higher levels of consumption. The rational consumer will make choices between the two goods to reach the highest indifference curve feasible given the choices available to her.

The theory of indifference curves was developed by Vilfredo Pareto and others in the first part of the 20th century. The theory was developed so that analysis of economic choices could be based upon preferences, which can be observed, rather than the older concept of utility which suffers from the disadvantage that it cannot be objectively measured.

Table of contents
1 Indifference Curve Properties
2 Example Indifference Curves

Indifference Curve Properties

Indifference curves are typically assumed to have the following features:

Assumptions

The first three assumptions are necessary, the next two are convenient.

Completeness: Consumers know their individual preferences; they can choose between any consumption bundle X and consumption bundle Y. They know either that X is preferred to Y, Y is preferred to X, or that they are indifferent between X and Y.

Transitivity: If a consumer prefers bundle X to bundle Y, and prefers bundle Y to bundle Z, then he must prefer bundle X to bundle Z.

Continuity: This means that you can choose to consume any amount of the good. For example, I could drink 11 mL of soda, or 12 mL, or 132 mL. I am not confined to drinking 2 liters or nothing. See also continuous function in mathematics.

Non-satiation: This is the idea that more of any good is always preferred to less.

Convexity: The marginal value a person gets from each commodity falls relative to the other good. In a two good world, if a consumer has relatively lots of one good he would be a happier with a little less of that good and a little more of the other.

Example Indifference Curves

Below is an example of three indifference curves:

The consumer would rather be on I3 than I2, and would rather be on I2 than I1, but does not care where they are on each indifference curve. The slope of an indifference curve, known by economists as the marginal rate of substitution, shows the rate at which consumers are willing to give up one good in exchange for more of the other good. For most goods the marginal rate of substitution is not constant so their indifference curves are curved. The curves are convex to the origin indicating a diminishing marginal rate of substitution.

If the goods are perfect substitutes then the indifference curves will be parallel lines since the consumer would be willing to trade at a fixed ratio. The marginal rate of substitution is constant.

If the goods are perfect complements then the indifference curves will be L-shaped. An example would be something like if you had a cookie recipe that called for 3 cups flour to 1 cup sugar. No matter how much extra flour you had, you still could not make more cookie dough without more sugar. Another example of perfect complements is a left shoe and a right shoe. The consumer is no better off having several right shoes if she has only one left shoe. Additional right shoes have zero marginal utility without more left shoes. The marginal rate of substitution is either zero or infinite.

Consumer theory uses indifference curves and budget constraints to produce consumer demand curves.

See also Bounded rationality, economics, Homo economicus, microeconomics, and consumer theory.