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Utility

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In the field of economics, utility is a measure of a person's satisfaction. It quantifies how much a person enjoys a specific state of the world. This concept helps researchers understand how individuals make choices. Economists use utility in two primary ways. In a normative context, utility is a goal or objective to maximize. This is often called an objective function. This view is linked to the work of moral philosophers. Jeremy Bentham and John Stuart Mill developed similar ideas regarding utilitarianism. In a descriptive context, utility refers to an apparent objective function. This function is revealed by observing how a person actually behaves.

A simple diagram of Indifference curve
A simple diagram of Indifference curve

A utility function is a mathematical tool used to represent preferences. It assigns a real number to different alternatives. If a person prefers alternative A over alternative B, then A receives a higher number. This allows someone to find the choice that maximizes their total utility. For example, a person named James might choose between apples and chocolates. A utility function can calculate the specific value of different combinations of these goods. Mathematician Gérard Debreu identified the conditions required for these functions to work. For a finite set of choices, the preferences must be complete and transitive. Completeness means a person can always choose between two options or say they are indifferent. Transitivity means if A is better than B, and B is better than C, then A is better than C.

There are two main ways to interpret the numbers in a utility function. These are known as cardinal and ordinal utility. Cardinal utility treats satisfaction as an objective, measurable quantity. It assumes utility can be measured like height or weight. In this view, the difference between two values is meaningful. For instance, if juice has 120 utils and tea has 80, the difference is 40. This magnitude helps economists analyze choices involving risk. Ordinal utility is different because it only focuses on the rank or order. It tells us that one option is preferred to another. However, it does not tell us how much more an individual enjoys it. In ordinal utility, the specific difference between numbers is considered behaviorally meaningless.

To visualize these preferences, economists use indifference curves. An indifference curve is a level curve of a utility function. It plots different combinations of two commodities, such as X and Y. All points along a single curve result in the same level of utility. This means an individual is indifferent between any two points on that line.

General version of budget constraint
General version of budget constraint

By combining these curves with budget constraints, economists can derive individual demand curves. A budget constraint shows the combinations of goods a person can actually afford. This helps model how people spend their limited resources to reach the highest satisfaction.

Economists also study the concept of marginal utility. Total utility is the satisfaction gained from an entire bundle of goods. Marginal utility is the change in total utility from consuming one additional unit of a good. It represents the slope of the utility function. Most models assume the principle of diminishing marginal utility. This means that as you consume more of a specific good, the extra satisfaction from each new unit decreases. For example, the first apple might provide great joy, but the tenth apple provides much less. This concept is vital for understanding how people distribute their spending.

Researchers use many different types of utility functions to model complex behaviors. Some common examples include constant elasticity of substitution (CES) and isoelastic utility. Other specialized forms include quasilinear utility and the Stone–Geary utility function. These mathematical models allow economists to test different assumptions about human nature. While most models assume utility is well-behaved, some preferences are harder to map. Lexicographic preferences are an example of a type that is not continuous. This makes them difficult to represent with a standard continuous utility function.

Utility theory connects to many broader fields of study. In welfare economics, utility is used to analyze Pareto efficiency. This concept looks at whether resources are distributed in a way that helps people without hurting others. Economists use Edgeworth boxes to illustrate these efficient contract curves. On a larger scale, utility can be used to create a social welfare function. This function aggregates individual utilities to study the well-being of an entire society. By studying these patterns, we gain insight into how individual choices shape the global economy.

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File:A simple diagram of Indifference curve.png
A simple diagram of Indifference curve.png
File:General version of budget constraint.png
General version of budget constraint.png
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