MARKET DEMANDMarket Demand CurvesSlide 3Slide 4Slide 5Slide 6Shifts in the Market Demand CurveShifts in Market DemandSlide 9Slide 10GeneralizationsSlide 12MARKET DEMANDMarket 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)•The first person’s demand for X isX1 = dX1(PX,PY,I1)•The second person’s demand for X isX2 = dX2(PX,PY,I2)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 incomeMarket 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 I2total X = X1 + X2total X = dX1(PX,PY,I1) + dX2(PX,PY,I2)total X = DX(PX,PY,I1,I2)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 slopingMarket Demand CurvesX XXPXPXPXdX1dX2X1*X2*PX*To derive the market demand curve, we sum the quantities demanded at every priceIndividual 1’sdemand curveIndividual 2’sdemand curveMarket demandcurveX*DXX1* + X2* = X*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Suppose that individual 1’s demand for oranges is given byX1 = 10 – 2PX + 0.1I1 + 0.5PY and individual 2’s demand isX2 = 17 – PX + 0.05I2 + 0.5PYThe market demand curve isX = X1 + X2 = 27 – 3PX + 0.1I1 + 0.05I2 + PYShifts 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 becomesX = 27 – 3PX + 4 + 1 + 4 = 36 – 3PXShifts in Market DemandIf PY rises to 6, the market demand curve shifts outward toX = 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 toX = 27 – 3PX + 3 + 1.5 + 4 = 35.5 – 3PX•Note that X is a normal good for both buyersGeneralizations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 IjXij = dij(P1,…,Pn, Ij)GeneralizationsThe market demand function for Xi is the sum of each individual’s demand for that good),...,,,...,(mnmjiijiPPDXX II111The market demand function depends on the prices of all goods and the incomes and preferences of all