UTILITY AND DEMAND 7CHAPTER

Objectives

After studying this chapter, you will able to Describe preferences using the concept of utility and

distinguish between total utility and marginal utility

Explain the marginal utility theory of consumer choice

Use marginal utility theory to predict the effects of changing prices and incomes

Explain the paradox of value

Household Consumption Choices

A household’s consumption choices are determined by:

Consumption possibilities

Preferences

Consumption Possibilities

A household’s consumption possibilities are constrained by its budget and the prices of the goods and services it buys.

A budget line describes the limits to a household’s consumption choices.

Household Consumption Choices

Figure 7.1 shows a budget line.

The household can afford all the points on or below the budget line.

The household cannot afford the points beyond the budget line.

Household Consumption Choices

Preferences

A household’s preferences determine the benefits or satisfaction a person receives consuming a good or service.

The benefit or satisfaction from consuming a good or service is called utility.

Total Utility

Total utility is the total benefit a person gets from the consumption of goods. Generally, more consumption gives more utility.

Household Consumption Choices

Table 7.1 on page 151 provides an example of total utility schedule.

Figure 7.2(a) shows a total utility curve.

Total utility increases with the consumption of a good.

Household Consumption Choices

Marginal Utility

Marginal utility is the change in total utility that results from a one-unit increase in the quantity of a good consumed.

As the quantity consumed of a good increases, the marginal utility from consuming it decreases.

We call this decrease in marginal utility as the quantity of the good consumed increases the principle of diminishing marginal utility.

Household Consumption Choices

Figure 7.2(b) illustrates diminishing marginal utility.

Utility is analogous to temperature.

Both are abstract concepts and both are measured in arbitrary units.

GDP (%)民間消費占 百分比

51.61

50.23

50.17

46.7

46.75

49.23

52.18

54.77

54.78

55.98

56.96

59.16

59.83

60.44

59.27

59.72

60.78

61.95

63.68

62.88

62.53

62.99

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GDP (%)民間消費占 百分比

Maximizing Utility

The key assumption of marginal utility theory is that the household chooses the consumption possibility that maximizes total utility.

The Utility-Maximizing Choice

We can find the utility-maximizing choice by looking at the total utility that arises from each affordable combination.

Table 7.2 (page 153) shows an example of the utility-maximizing combination, which is called a consumer equilibrium.

Maximizing Utility

Equalizing Marginal Utility per Dollar Spent

Using marginal analysis, a consumer’s total utility is maximized by following the rule:

Spend all available income and equalize the marginal utility per dollar spent on all goods.

The marginal utility per dollar spent is the marginal utility from a good divided by its price.

Maximizing Utility

Call the marginal utility of movies MUM

Call the marginal utility of soda MUS

Call the price of movies PM

Call the price of soda PS

The marginal utility per dollar spent on movies is MUM/PM

The marginal utility per dollar spent on soda is MUS/PS.

Maximizing Utility

Total utility is maximized when:

MUM/PM = MUS/PS

Table 7.3 (page 154) and Figure 7.3 on the next slide show why the utility maximizing rule works.

Maximizing Utility

If MUM/PM > MUS/PS, then moving a dollar from soda to movies increases the total utility from movies by more than it decreases the total utility from soda, so total utility increases.

Only when MUM/PM = MUS/PS, is it not possible to reallocate the budget and increase total utility.

Maximizing Utility

Similarly, if MUS/PS > MUM/PM, then moving a dollar from movies to soda increases the total utility from soda by more than it decreases the total utility from movies, so total utility increases. Again, only when MUM/PM

= MUS/PS, is it not possible to reallocate the budget and increase total utility.

Predictions of Marginal Utility Theory

A Fall in the Price of a Movie

When the price of a good falls the quantity demanded of that good increases—the demand curve slopes downward.

For example, if the price of a movie falls, we know that MUM/PM rises, so before the consumer changes the quantities consumed, MUM/PM > MUS/PS.

To restore consumer equilibrium (maximum total utility) the consumer increases the quantity of movies consumed to drive down the MUM and restore MUM/PM = MUS/PS.

Predictions of Marginal Utility Theory

A change in the price of one good changes the demand for another good.

You’ve seen that if the price of a movie falls, MUM/PM rises, so before the consumer changes the quantities consumed, MUM/PM > MUS/PS.

To restore consumer equilibrium (maximum total utility) the consumer decreases the quantity of soda consumed to drive up the MUS and restore MUM/PM = MUS/PS.

Predictions …

Table 7.4 and Figure 7.4 illustrate these predictions.

A fall in the price of a movie increases the quantity of movies demanded—a movement along the demand curve for movies,

and decreases the demand for soda—a shift of the demand curve for soda.

Predictions of Marginal Utility Theory

A Rise in the Price of Soda

Now suppose the price of soda rises.

We know that MUS/PS falls, so before the consumer changes the quantities consumed, MUS/PS < MUM/PM.

To restore consumer equilibrium (maximum total utility) the consumer decreases the quantity of soda consumed to drive up the MUS and increases the quantity of movies consumed to drive down MUM. These changes restore MUM/PM = MUS/PS.

Predictions …

Table 7.5 and Figure 7.5 illustrate these predictions.

A rise in the price of soda decreases the quantity of soda demanded—a movement along the demand curve for soda,

and increases the demand for movies—a shift of the demand curve for movies.

Predictions of Marginal Utility Theory

A Rise in Income

When income increases, the demand for a normal good increases.

Table 7.6 illustrate this prediction

Table 7.7 summarizes the assumptions and predictions of marginal utility theory.

Predictions of Marginal Utility Theory

Individual Demand and Market Demand

The market demand for a good is the relationship between the price of the good and total quantity demanded of that good.

The individual demand for a good is the relationship between the price of the good and the quantity demanded by one person.

Figure 7.6 on the next slide shows how we sum the individual demand curves to obtain the market demand.

Predictions of Marginal Utility Theory

Predictions of Marginal Utility Theory

Marginal Utility and Elasticity

We can predict the price elasticity of demand for a good by knowing the characteristics of the marginal utility of the good.

If as the quantity consumed, marginal utility diminishes rapidly, then a given price change will bring a small quantity change to restore consumer equilibrium, and demand will be inelastic.

Efficiency, Price, and Value

Consumer Efficiency and Consumer Surplus

When consumers maximize their utility, they are using resources efficiently.

And the marginal benefit from a good or service is the maximum price the consumer is willing to pay for an extra unit of that good or service when his or her utility is maximized.

Efficiency, Price, and Value

The Paradox of Value

The paradox of value “Why is water, which is essential to life, far cheaper than diamonds, which are not essential?” is resolved by distinguishing between total utility and marginal utility.

Figure 7.7 on the next slide illustrates the resolution of the paradox.

Efficiency, Price, and Value

The total utility and consumer surplus from water is large but the marginal utility and price of water is small.

In contrast, the total utility and consumer surplus from diamonds is small but the marginal utility and price of a diamond is large.

THE END