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Chapter 4

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

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  1. Chapter 4 Market Demand and Elasticity

  2. 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.

  3. 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.

  4. FIGURE 4.1: Constructing a Market Demand Curve from Individual Demand Curves PX P* X 0 X* 1 (a) Individual 1

  5. 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

  6. Construction of the Market Demand Curve • 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.

  7. 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

  8. Shifts in the Market Demand Curve • 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.

  9. Shifts in the Market Demand Curve • 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

  10. 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

  11. 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

  12. Shifts in the Market Demand Curve • 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.

  13. Shifts in the Market Demand Curve • 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.

  14. Shifts in the Market Demand Curve • 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.

  15. A Word on Notation and Terms • 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.

  16. Elasticity • 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.

  17. Elasticity • 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.

  18. Price Elasticity of Demand • 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

  19. Price Elasticity of Demand • 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.

  20. Values of the Price Elasticity of Demand • 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

  21. TABLE 4.1: Terminology for the Ranges of eQ,P

  22. Price Elasticity and the Shape of the Demand Curve • 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.

  23. Price Elasticity and the Substitution Effect • 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.

  24. Price Elasticity and the Substitution Effect • 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.

  25. Price Elasticity and Time • 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.

  26. APPLICATION 4.2: Brand Loyalty • 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.

  27. APPLICATION 4.2: Brand Loyalty • 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.

  28. Price Elasticity and Total Expenditures • 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.

  29. Price Elasticity and Total Expenditures • 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.

  30. Price Elasticity and Total Expenditures • 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.

  31. TABLE 4.2: Relationship between Price Changes and Changes in Total Expenditure

  32. APPLICATION 4.3: Volatile Farm Prices • 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.

  33. Demand Curves and Price Elasticity • 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.

  34. Linear Demand Curves and Price Elasticity • 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.

  35. 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.

  36. FIGURE 4.3: Elasticity Varies along a Linear Demand Curve Price (dollars) 50 40 30 25 Demand 20 10 0 20 40 50 60 80 100 Quantity of tape players per week

  37. TABLE 4.3: Price, Quantity, and Total Expenditures on Walkmans for the Demand Function Q = 100 - 2P

  38. 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.

  39. Elasticity of a Straight Line Demand Curve • More generally, for a linear demand curve of the form Q = a - bP,

  40. A Unitary Elastic 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.

  41. General Formula for the Elasticity of a Hyperbola • If the demand curve takes the following form, the price elasticity of demand is equal to b everywhere on the curve.

  42. FIGURE 4.4: A Unitary Elastic Demand Curve Price (dollars) 60 50 40 30 20 20 24 30 40 60 Quantity of tape players per week

  43. Income Elasticity of Demand • 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):

  44. Income Elasticity of Demand • 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.

  45. APPLICATION 4.4: An Experiment in Health Insurance • 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.

  46. The Moral Hazard Problem • 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?

  47. The Rand Experiment • 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.

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

  49. Table 1: Results of the Rand Health Insurance Experiment

  50. Low Elasticities for Hospital and Doctors’ Visits • 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.

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