(第八版)微观经济学：现代观点.ppt

Chapter TwoBudget Constraint预算约束1Structure of chapter 2n2.1 The definition and properties of budget constraintqAlgebraqGraphn2.2.Changes in budget constraintn2.3.Government taxes and their effect on budget constraint.22.1 The Budget ConstraintnA consumption set（消费集,X）is the set of all consumption bundles that the consumer can conceive.3Consumption Bundle（消费束）nA consumption bundle x=(x1,x2,xn)is a vector containing different quantities of each of the n commodities.qx1 units of commodity 1,x2 units of commodity 2 and so on up to xn units of commodity n.nNon negative constraint:X=(x1,xn)|x1 0,xn 0 4Budget constraintnCommodity prices are(p1,p2,pn)nConsumers income:m.nQ:When is a bundle(x1,xn)affordable at prices p1,pn?nA:When p1x1+pnxn mwhere m is the consumers(disposable)income.nBudget constraint:the amount of money spent on the n goods cannot be more than the consumers income.5Budget SetnThe consumers budget set（预算集）consists of all bundles of goods that are affordable at given prices and income.nB(p1,pn,m)=(x1,xn)|x1 0,xn 0 and p1x1+pnxn m 6Budget linenBudget line:the consumption bundles that cost exactly m.nThe budget line is the upper boundary of the budget set.nTo show the budget line with a graph,we assume that the consumption bundle consists only of two goods,x1 and x2.nx2 is composite good(复合商品),which is measured in dollars to be spent on goods other than good 1.7Budget Set and Budget Linex2x1Budget line isp1x1+p2x2=m.m/p1BudgetSetm/p28Budget linex2x1p1x1+p2x2=m.m/p2m/p19Properties of the budget linenInterceptsnunaffordable naffordablenjust affordable10Affordablex2x1m/p1m/p211Slope of the budget linex2x1Slope is-p1/p2+1-p1/p212Meaning of the SlopenIncreasing x1 by 1 unit must reduce x2 by p1/p2.nOpportunity cost of consuming one unit of x1nWhat is the Opportunity cost of consuming one unit of x2?13The slope of budget line:an exampleMoviesCDsnSlope=-PC/PM:qHow many extra units of movies a consumer can buy by sacrificing a unit of CD.nIf a CD costs$10 and a Movie costs$20,if you give up one CD,how many movies can you buy?m/pm/pMMm/pm/pC C M/M/C=-PC=-PC C/P/PMM142.2 How the budget line changesnThe budget set and budget line depend upon prices and income.n What happens as prices or income change?152.2.1 A change in incomenIncreases in income m shift the budget line outward in a parallel manner,thereby enlarging the budget set.nDecreases in income m shift the budget line inward in a parallel manner,thereby shrinking the budget set.162.2.2 A change in pricesnWhat happens if just one price changes?nWhat happens if two price changes?17A decrease in p1:from p1 to p1”?Originalbudget setx2x1m/p2m/p1m/p1”New affordable choices-p1/p218A decrease in p1:from p1 to p1”?Originalbudget setx2x1m/p2m/p1m/p1”New affordable choicesBudget constraint pivots;slope flattens from-p1/p2 to -p1”/p2-p1/p2-p1”/p219The effect of a change in one pricenReducing the price of one commodity pivots the budget line outward.nIncreasing one price pivots the budget line inwards.nQ:What happens if both prices change?20The effect of a change in both pricesnSuppose both prices become t times as large:qMultiplying both prices by t is just like dividing income by t.qIf we multiply both prices and income by t,the budget line wont change at all.21Relative PricesnThe budget linep1x1+p2x2=mnCan be equivalently expressed as p1/p2 x1+x2=m/p2np2=1:numeraire price(基准价格),it defines all prices relative to p2nx2 is composite good.22 Suppose m=$60,PCD=$3,PM=$6.n1)Please draw the budget line,what is the slope of the budget line?n2)If income decreases to$30,what happens to the budget line?n3)If PCD increases to$6,how does the budget line change?n4)What happens if PCD,PM and m have all doubled?Example232.3 Various government taxesnQuantity tax(从量税):the consumer has to pay a certain amount to the government for each unit of the good he purchases.q on x:(p+t)x(the price of the good changes from p to p+t).qFrom the viewpoint of the consumer,the tax is just like a higher price.24nValue tax(or ad valorem tax or sales tax)(从价税):Value tax is a tax on value(p),usually expressed in percentage terms.qon p:(1+t)p.nLump sum tax(总额税,T):the government takes away some fixed amount of money,regardless of the individuals behavior.nQuantity and value taxes tilt the budget line while a lump sum tax shifts the budget line inward.nTaxes and subsidies affect prices in exactly the same way except for the sign.25Value tax and lump sum tax nSuppose a value tax levied at a rate of 5%,then price increases from p to(1+0.05)p=1.05p.nA uniform value levied at a rate of t increases the prices of commodities by tp from p to(1+t)p.nA uniform value tax levied at rate t is equivalent to an income tax levied at rate 26Government programs and their effect on budget constraintnRationingnFood stamp program27Rationing(定量配给)nRationing means that the level of consumption of some good is fixed to be no larger than some amount.nE.g.during the world war II,the U.S.government rationed certain foods like butter and meat.nQ:suppose good 1 is rationed so that x1x1*,How it will change the budget constraint?28The Food Stamp Program（食品券补贴政策）nSince 1964 the U.S.federal government has provided a subsidy on food for poor people.nFood stamps are coupons that can be legally exchanged only for food.nHow does a food stamp change a familys budget constraint?29The pre-1979 Food Stamp Program n It was an ad valorem subsidy on food.nSuppose m=$100,x1 is food and x2 is a composite good,so p2=$1.nNow the household is allowed to buy$153 of food stamps for$25.nAssume that the consumer is not permitted to sell the food stamps,how will the budget constraint change?30The Post-1979 Food Stamp ProgramnThe government simply given the food stamp to the qualified households.nSuppose that a household now receives a grant of$200 of food stamps a month.nHow will the budget constraint change?31The Comparison of the Two Programs Part A shows the pre-1979 program and part B the post-1979 program.32