Market demand
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MARKET DEMAND. Market demand refers to the various quantities per unit of time that buyers are willing and able to buy at all alternative prices, other things being equal. Market Demand Curves. Assume that there are only two goods ( X and Y ) and two individuals (1 and 2)

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MARKET DEMAND

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Market demand

MARKET DEMAND

Market demand refers to the various quantities per unit of time that buyers are willing and able to buy at all alternative prices, other things being equal.


Market demand curves

Market Demand Curves

  • Assume that there are only two goods

    (X and Y) and two individuals (1 and 2)

    • The first person’s demand for X is

      X1 = dX1(PX,PY,I1)

    • The second person’s demand for X is

      X2 = dX2(PX,PY,I2)


Market demand curves1

Market Demand Curves

  • Features of these demand curves:

    • Both individuals are assumed to face the same prices

    • Each buyer is assumed to be a price taker

      • must accept the prices prevailing in the market

    • Each person’s demand depends on his or her own income


Market demand curves2

Market Demand Curves

  • The total demand for X is the sum of the amounts demanded by the two buyers

    • The demand function will depend on PX, PY, I1, and I2

      total X = X1 + X2

      total X = dX1(PX,PY,I1) + dX2(PX,PY,I2)

      total X = DX(PX,PY,I1,I2)


Market demand curves3

Market Demand Curves

  • To construct the market demand curve, PX is allowed to vary while PY, I1, and I2 are held constant

  • If each individual’s demand for X is downward sloping, the market demand curve will also be downward sloping


Market demand curves4

PX*

DX

X2*

X*

X1*

X1* + X2* = X*

Market Demand Curves

To derive the market demand curve, we sum the quantities demanded at every price

PX

PX

PX

Individual 1’s

demand curve

Individual 2’s

demand curve

Market demand

curve

dX1

dX2

X

X

X


Shifts in the market demand curve

Shifts in the MarketDemand Curve

  • The market demand summarizes the ceteris paribus relationship between X and PX

    • Changes in PX result in movements along the curve (change in quantity demanded)

    • Changes in other determinants of the demand for X cause the demand curve to shift to a new position (change in demand)


Shifts in market demand

Shifts in Market Demand

  • Suppose that individual 1’s demand for oranges is given by

    X1 = 10 – 2PX + 0.1I1 + 0.5PY

    and individual 2’s demand is

    X2 = 17 – PX + 0.05I2 + 0.5PY

  • The market demand curve is

    X = X1 + X2 = 27 – 3PX + 0.1I1 + 0.05I2 + PY


Shifts in market demand1

Shifts in Market Demand

  • To graph the demand curve, we must assume values for PY, I1, and I2

  • If PY = 4, I1 = 40, and I2 = 20, the market demand curve becomes

    X = 27 – 3PX + 4 + 1 + 4 = 36 – 3PX


Shifts in market demand2

Shifts in Market Demand

  • If PY rises to 6, the market demand curve shifts outward to

    X = 27 – 3PX + 4 + 1 + 6 = 38 – 3PX

    • Note that X and Y are substitutes

  • If I1 fell to 30 while I2 rose to 30, the market demand would shift inward to

    X = 27 – 3PX + 3 + 1.5 + 4 = 35.5 – 3PX

    • Note that X is a normal good for both buyers


Generalizations

Generalizations

  • Suppose that there are n goods (Xi, i = 1,n) with prices Pi, i = 1,n.

  • Assume that there are m individuals in the economy

  • The j th’s demand for the i th good will depend on all prices and on Ij

    Xij = dij(P1,…,Pn, Ij)


Generalizations1

Generalizations

  • The market demand function for Xi is the sum of each individual’s demand for that good

  • The market demand function depends on the prices of all goods and the incomes and preferences of all buyers


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