Reading: Marginal Utility

Choices Are Made at the Margin

Economists argue that most choices are made “at the margin.” The margin is the current level of an activity. Think of it as the edge from which a choice is to be made. A choice at the margin is a decision to do a little more or a little less of something.

Assessing choices at the margin can lead to extremely useful insights. Consider, for example, the problem of curtailing water consumption when the amount of water available falls short of the amount people now use. Economists argue that one way to induce people to conserve water is to raise its price. A common response to this recommendation is that a higher price would have no effect on water consumption, because water is a necessity. Many people assert that prices do not affect water consumption because people “need” water.

But choices in water consumption, like virtually all choices, are made at the margin. Individuals do not make choices about whether they should or should not consume water. Rather, they decide whether to consume a little more or a little less water. Household water consumption in the United States totals about 105 gallons per person per day. Think of that starting point as the edge from which a choice at the margin in water consumption is made. Could a higher price cause you to use less water brushing your teeth, take shorter showers, or water your lawn less? Could a higher price cause people to reduce their use, say, to 104 gallons per person per day? To 103? When we examine the choice to consume water at the margin, the notion that a higher price would reduce consumption seems much more plausible. Prices affect our consumption of water because choices in water consumption, like other choices, are made at the margin.

The elements of opportunity cost, maximization, and choices at the margin can be found in each of two broad areas of economic analysis: microeconomics and macroeconomics. Your economics course, for example, may be designated as a “micro” or as a “macro” course. We will look at these two areas of economic thought in the next section.

Marginal utility is based on the notion that individuals rarely face all-or-nothing decisions, that most of the time they are considering a little more or a little less of something when allocating their budget, time or other scarce resources. So a student might ask, “how much better will I do on an exam if I study for one more hour?” The answer could be called the marginal grade improvement. Economists use a number of marginal concepts. The marginal utility of a third slice of pizza is the change in satisfaction one gets when eating the third slice instead of stopping with two. The marginal cost of one more unit of output a firm produces is the amount that total cost increases when the firm produces one more unit of output.

The general formula for computing a marginal item is the change in the outcome divided by the change in the number of inputs used to produce that outcome. For example, if two more hours of work yields an additional $20 in wages, the marginal wage earned is $20/2 hours = $10 per hour.

Law of Diminishing Marginal Utility

Watch this lecture video clip to learn more about why when we consume even more of a good, the marginal benefit of that good decreases with each additional good.

Self Check: Marginal Utility

Answer the question(s) below to see how well you understand the topics covered in the previous section. This short quiz does not count toward your grade in the class, and you can retake it an unlimited number of times.

You’ll have more success on the Self Check if you’ve completed the Reading in this section.

Use this quiz to check your understanding and decide whether to (1) study the previous section further or (2) move on to the next section.