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Chapter 4. Market Demand and Elasticity. Market Demand Curves. The market demand is the total quantity of a good or service demanded by all potential buyers .

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Chapter 4

Chapter 4

Market Demand and Elasticity


Market demand curves
Market Demand Curves

  • The market demand is the total quantity of a good or service demanded by all potential buyers.

  • The market demand curve is the relationship between the total quantity demanded of a good or service and its price, holding all other factors constant.


Construction of the market demand curve
Construction of the Market Demand Curve

  • The market demand curve is constructed by horizontally summing the demands of the individual consumers

  • Assume the market consists of only two buyers as shown in Figure 4.1

    • At any given price, such as P*X, individual 1 demands X*1 and individual 2 demands X*2.


Figure 4 1 constructing a market demand curve from individual demand curves
FIGURE 4.1: Constructing a Market Demand Curve from Individual Demand Curves

PX

P*

X

0

X*

1

(a) Individual 1


Figure 4 1 constructing a market demand curve from individual demand curves1
FIGURE 4.1: Constructing a Market Demand Curve from Individual Demand Curves

PX

PX

P*

X

0

X*

0

X*

1

2

(a) Individual 1

(b) Individual 2


Construction of the market demand curve1
Construction of the Market Demand Curve Individual Demand Curves

  • The total quantity demanded at the market at P*X is the sum of the two amounts: X* = X*1 + X*2 .

  • The point X*, P*X is one point on the market demand curve.

  • The other points on the curve are similarly plotted.


  • Figure 4 1 constructing a market demand curve from individual demand curves2
    FIGURE 4.1: Constructing a Market Demand Curve from Individual Demand Curves

    PX

    PX

    PX

    P*

    X

    D

    0

    X*

    0

    X*

    0

    X*

    X

    1

    2

    (a) Individual 1

    (b) Individual 2

    (c) Market Demand


    Shifts in the market demand curve
    Shifts in the Market Demand Curve Individual Demand Curves

    • To discover how some event might shift a market demand curve, we must first find out how this event causes individual demand curves to shift and then compare the horizontal sum of these new demand curves with the old demand curve.


    Shifts in the market demand curve1
    Shifts in the Market Demand Curve Individual Demand Curves

    • For example consider the two buyer case where both consumers regard X as a normal good.

    • An increase in income for each consumer would shift their individual demand curves out so that the market demand curve, would also shift out

    • This situation is shown in Figure 4.2


    Figure 4 2 increases in each individual s income cause the market demand curve to shift outward
    FIGURE 4.2: Increases in Each individual’s Income Cause the Market Demand Curve to Shift Outward

    PX

    PX

    PX

    D

    P*

    X

    0

    X*

    0

    X*

    0

    X*

    X

    1

    2

    (a) Individual 1

    (b) Individual 2

    (c) Market Demand


    Figure 4 2 increases in each individual s income cause the market demand curve to shift outward1
    FIGURE 4.2: Increases in Each individual’s Income Cause the Market Demand Curve to Shift Outward

    PX

    D’

    PX

    PX

    D

    P*

    X

    0

    X*

    X**

    0

    X*

    X**

    0

    X*

    X**

    X

    1

    1

    2

    2

    (a) Individual 1

    (b) Individual 2

    (c) Market Demand


    Shifts in the market demand curve2
    Shifts in the Market Demand Curve the Market Demand Curve to Shift Outward

    • However, some events result in ambiguous outcomes.

      • If one consumer’s demand curve shifts out while another’s shifts in, the net effect depends on the size of the relative shifts.

    • An increase in income for pizza lovers would increase the market demand for pizza so long as it is a normal good.


    Shifts in the market demand curve3
    Shifts in the Market Demand Curve the Market Demand Curve to Shift Outward

    • On the other hand, if the increase in income was for people who don’t like pizza, there would be no significant effect on the market demand curve for pizza.

    • Changes in the prices of related goods, substitutes or complements, will also shift the individual and market demand curves.


    Shifts in the market demand curve4
    Shifts in the Market Demand Curve the Market Demand Curve to Shift Outward

    • If goods X and Y are substitutes, an increase in the price of Y will increase the demand for X. Similarly, a decrease in the price of Y will decrease the demand for X.

    • If goods X and Y are complements, an increase in the price of Y will decrease the demand for X. A decrease in the price of Y will increase the demand for X.


    A word on notation and terms
    A Word on Notation and Terms the Market Demand Curve to Shift Outward

    • When looking at only one market, Q is used for the quantity of the good demanded, and P is used for its price.

    • When drawing the demand curve, all non-price factors are assumed to not change.

    • Movements along the curve are changes in quantity demanded, while shifts are changes in demand.


    Elasticity
    Elasticity the Market Demand Curve to Shift Outward

    • Goods are often measured in different units (steak is measured in pounds while oranges are measured in dozens).

    • It can be difficult to make simple comparisons between goods when trying to determine which is more responsive to changes in price.


    Elasticity1
    Elasticity the Market Demand Curve to Shift Outward

    • Elasticity is a measure of the percentage change in one variable brought about by a 1 percent change in some other variable.

    • Since it is measured in percentages, the units cancel out so that it is a unit-less measure of responsiveness.


    Price elasticity of demand
    Price Elasticity of Demand the Market Demand Curve to Shift Outward

    • The price elasticity of demand is the percentage change in the quantity demanded of a good in response to a 1 percent change in its price


    Price elasticity of demand1
    Price Elasticity of Demand the Market Demand Curve to Shift Outward

    • The price elasticity records how Q changes in percentage terms in response to a percentage change in P.

    • Since, on a typical demand curve, P and Q move oppositely, eQ,Pwill be negative.

    • For example, if eQ,P= -2, a 1 percent increase in price leads to a 2 percent decline in quantity.


    Values of the price elasticity of demand
    Values of the Price Elasticity of Demand the Market Demand Curve to Shift Outward

    • When eQ,P< -1, the quantity demanded is relatively unresponsive to changes in price inelastic

    • When eQ,P = -1, a price increase causes a proportional quantity decrease, and the curve is called unit elastic.

    • When eQ,P > -1, a price increase causes more than a proportional quantity decrease, and the curve is called elastic


    Table 4 1 terminology for the ranges of e q p
    TABLE 4.1: Terminology for the Ranges of the Market Demand Curve to Shift OutwardeQ,P


    Price elasticity and the shape of the demand curve
    Price Elasticity and the Shape of the Demand Curve the Market Demand Curve to Shift Outward

    • We often classify market demand curves by their elasticities

      • For example, the market demand curve for medical services is inelastic (nearly vertical) since there is little quantity response to changes in price.

      • Alternatively, the market demand curve for a single type of candy bar is very responsive to price change (nearly flat) and is very elastic.


    Price elasticity and the substitution effect
    Price Elasticity and the Substitution Effect the Market Demand Curve to Shift Outward

    • Goods which have many close substitutes are subject to large substitution effects from a price change so their market demand curve is likely to be relatively elastic.

    • Goods with few close substitutes, on the other hand, will likely be relatively inelastic.


    Price elasticity and the substitution effect1
    Price Elasticity and the Substitution Effect the Market Demand Curve to Shift Outward

    • There is also an income effect that will determine how responsive quantity demanded is to changes in price.

    • However, since changes in the prices of most goods have a small effect on individuals’ real incomes, the income effect will likely not have as large an impact on elasticity as the substitution effect.


    Price elasticity and time
    Price Elasticity and Time the Market Demand Curve to Shift Outward

    • Some items can be quickly substituted for, such as a brand of breakfast cereal, others, such as heating fuel, may take several years.

    • Thus, in some situations, it is important to make the distinction between the short-term and long-term elasticities of demand.


    Application 4 2 brand loyalty
    APPLICATION 4.2: Brand Loyalty the Market Demand Curve to Shift Outward

    • Substitution due to price changes will likely take a longer time if individual’s develop spending habits.

    • Such brand loyalties are rational since they reduce decision making costs.

    • Over the long term, however, price differences may cause buyers to try other brands.


    Application 4 2 brand loyalty1
    APPLICATION 4.2: Brand Loyalty the Market Demand Curve to Shift Outward

    • It took several years, but by the 1970s the price differences between U.S. and Japanese cars eventually convinced Americans to buy the Japanese cars.

    • Brand name Licensing, such as Coca-Cola sweatshirts and Mickey Mouse watches, makes products that were previously nearly perfect substitutes, now much less so.


    Price elasticity and total expenditures
    Price Elasticity and Total Expenditures the Market Demand Curve to Shift Outward

    • Total expenditures on a good are found by multiplying the good’s price (P) times the quantity purchased (Q).

    • When demand is elastic, price increases will cause total expenditures to fall.

      • Total expenditures on the product decreases as the price goes up.


    Price elasticity and total expenditures1
    Price Elasticity and Total Expenditures the Market Demand Curve to Shift Outward

    • For example suppose price elasticity = -1.5.

      • Suppose a family buys 100 pounds of chicken per year at a price of $2 per pound. The price elasticity of demand for chicken is -1.5. If the price of chicken increases to $2.20 (a 10% increase). What is the difference between new family’s expenditures on chicken and the old one? The family’s consumption of chicken falls to 85 pounds a year (a 15% decrease). Total expenditure on chicken will also fall, from $200 (100 pounds x $2 per pound) to $187 (85 pounds x $2.20 per pound). The difference is -$13.


    Price elasticity and total expenditures2
    Price Elasticity and Total Expenditures the Market Demand Curve to Shift Outward

    • Of course, when demand is inelastic and prices increase, total expenditures increase.

      • A family currently uses 1000 gallons of gasoline a year when the price is $1 per gallon; Suppose that the price elasticity of demand for gasoline is -0.5. If the price of gasoline increases to $1.10 (10% increase). What happen to expenditure on gasoline? The Consumption of gasoline falls to 950 gallons (5% decrease). Total expenditure on gasoline increase from $1000 (1000 gallons x $1/ gallon) to $1045 (950 gallons x $1.1/ gallon)

    • With unit elasticity, total expenditures remain the same with a price change.

      • The movement in one direction by the price is fully offset by the movement in the other direction with the quantity demanded.



    Application 4 3 volatile farm prices
    APPLICATION 4.3: Volatile Farm Prices Total Expenditure

    • The demand for many basic agricultural products (wheat, corn, etc.) is relatively inelastic.

    • Even modest changes in supply, brought about by weather patterns, can have large effects on crop prices.


    Demand curves and price elasticity
    Demand Curves and Price Elasticity Total Expenditure

    • The relationship between a particular demand curve and the price elasticity it exhibits can be complicated.

    • For some curves, the elasticity remains constant everywhere, but for others it is different at every point.

    • A more accurate way to describe it would be to say the elasticity is for current prices.


    Linear demand curves and price elasticity
    Linear Demand Curves and Price Elasticity Total Expenditure

    • The price elasticity of demand is always changing along a straight line demand curve.

      • Demand is elastic at prices above the midpoint price.

      • Demand is unit elastic at the midpoint price.

      • Demand is inelastic at prices below the midpoint price.


    Numerical example of elasticity on a straight line demand curve
    Numerical Example of Elasticity on a Straight Line Demand Curve

    • Assume a straight-line demand curve for Walkman cassette tape players is Q = 100 - 2P

      • where Q is the quantity of players demanded per week and P is their price.

    • This demand curve is illustrated in Figure 4.3 and Table 4.3 shows several price-quantity combinations.


    Figure 4 3 elasticity varies along a linear demand curve
    FIGURE 4.3: Elasticity Varies along a Linear Demand Curve Curve

    Price

    (dollars)

    50

    40

    30

    25

    Demand

    20

    10

    0

    20

    40

    50

    60

    80

    100

    Quantity of tape

    players per week


    Table 4 3 price quantity and total expenditures on walkmans for the demand function q 100 2p
    TABLE 4.3: Price, Quantity, and Total Expenditures on Walkmans for the Demand Function Q = 100 - 2P


    Numerical example of elasticity on a straight line demand curve1
    Numerical Example of Elasticity on a Straight Line Demand Curve

    • For prices of $50 or more, nothing is bought so total expenditures are $0.

    • As prices fall between $50 and $25, the midpoint, total expenditures increase.

    • At the midpoint, total expenditures reach a maximum.

    • As prices fall below $25, total expenditures also fall.


    Elasticity of a straight line demand curve
    Elasticity of a Straight Line Demand Curve Curve

    • More generally, for a linear demand curve of the form Q = a - bP,


    A unitary elastic curve
    A Unitary Elastic Curve Curve

    • Suppose the demand for tape players took the form

    • The graph of this equation, shown in Figure 4.4, is a hyperbola.

    • P·Q = $1,200 regardless of price so demand is unit elastic (-1) everywhere on the curve.


    General formula for the elasticity of a hyperbola
    General Formula for the Elasticity of a Hyperbola Curve

    • If the demand curve takes the following form, the price elasticity of demand is equal to b everywhere on the curve.


    Figure 4 4 a unitary elastic demand curve
    FIGURE 4.4: A Unitary Elastic Demand Curve Curve

    Price

    (dollars)

    60

    50

    40

    30

    20

    20

    24

    30

    40

    60

    Quantity of

    tape players

    per week


    Income elasticity of demand
    Income Elasticity of Demand Curve

    • The income elasticity of demand equals the percentage change in the quantity demanded of a good in response to a 1 percent change in income.

    • The formula is given by (where I represents income):


    Income elasticity of demand1
    Income Elasticity of Demand Curve

    • For normal goods, eQ,I is positive because increases in income lead to increases in purchases of the good.

    • For inferior goodseQ,I is negative.

    • If eQ,I > 1, the purchase of the good increases more rapidly than income so the good might be called a luxury good.


    Application 4 4 an experiment in health insurance
    APPLICATION 4.4: An Experiment in Health Insurance Curve

    • Most developed countries have some form of national health insurance.

      • In the U.S. Medicare covers the elderly and Medicaid is available for many of the poor.

    • Recently a number of comprehensive government health plans have been proposed.


    The moral hazard problem
    The Moral Hazard Problem Curve

    • A “moral hazard” problem occurs because insurance misleadingly lowers the out-of-pocket expenses to patients, greatly increasing their demand for medical services.

    • An important question, in considering implementing national health insurance is how large an increase is likely to develop?


    The rand experiment
    The Rand Experiment Curve

    • The Rand Corporation conducted a government-funded large-scale experiment in four cities.

    • People were assigned to different insurance plans that varied in the generosity of coverage they offered.

    • Table 1 shows the results from the experiment.


    The rand experiment1
    The Rand Experiment Curve

    • A rough estimate of the elasticity of demand can be obtained by averaging the percentage changes across the various plans in Table 1



    Low elasticities for hospital and doctors visits
    Low Elasticities for Hospital and Doctors’ Visits Curve

    • Using the estimate of -0.22 found in Table 4.4, and based on other studies suggests only a small increase in hospital and doctor visits would result from the lower prices provided by insurance.

    • Alternatively, researchers have found greater elasticities (around -0.5) for dental care and outpatient mental health care.


    Cross price elasticity of demand
    Cross-Price Elasticity of Demand Curve

    • The cross-price elasticity of demand measures the percentage change in the quantity demanded of a good in response to a 1 percent change in the price of another good. Letting P’ be the price of another good,


    Cross price elasticity of demand1
    Cross-Price Elasticity of Demand Curve

    • If the goods are substitutes, an increase in the price of one will cause buyers to purchase more of the substitute, so the elasticity will be positive.

    • If the goods are complements, an increase in the price of one will cause buyers to buy less of that good and also less of the good they use with it, so the elasticity will be negative


    Empirical studies of demand estimating demand curves
    Empirical Studies of Demand: Estimating Demand Curves Curve

    • Estimating a demand curve for a product is one of the more difficult but important problems in econometrics.

    • Empirical studies are useful because they a provide a more precise estimate of the amount of change in quantity demanded that results due to a price change.


    Problems estimating demand curves
    Problems Estimating Demand Curves Curve

    • The first problem is how to derive an estimate holding all other factors (the ceteris paribus assumption) constant.

    • This problem is often solved, as discussed in the Appendix to Chapter 1, by the use of multiple regression analysis.


    Problems estimating demand curves1
    Problems Estimating Demand Curves Curve

    • The second problem deals with what is observed in the data. The data points represent quantity and price outcomes that are simultaneously determined by both the demand and the supply curves.

    • The econometric problem is to “identify” from these equilibrium points the demand curve that generated them.


    Some elasticity estimates
    Some Elasticity Estimates Curve

    • Table 4.4 gathers a number of estimated income and price elasticities of demand.

    • Some things to note

      • All of the estimated price elasticities are less than zero as predicted by a negatively sloped demand curve.

      • Most of the price elasticity estimates are inelastic.



    Some elasticity estimates1
    Some Elasticity Estimates Demand

    • The income elasticities of automobiles and transatlantic travel exceed 1 (luxuries).

    • The high income elasticities are balanced by goods such as food and medical care which are less than 1 (necessities).

    • There is no evidence of Giffen’s paradox in the table.


    Some cross price elasticity estimates
    Some Cross-price Elasticity Estimates Demand

    • Table 4.5 shows a few cross-price elasticity estimates

    • All of the goods appear to be substitutes and have positive cross-price elasticities.



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