新古典增长模型

Download free ebooks at bookboon.com Pl ea se c lic k th e ad ve rt Neoclassical Growth Model and Ricardian Equivalence 2 Contents 1. Introduction 2. The neoclassical growth model 3. The steady state 4. Ricardian equivalence 5. Conclusions Appendix A A1. The maximization problem of the representative fi rm A2. The equilibrium value of the representative fi rm A3. The goverment’s intertemporal budget constraint A4. The representative household’s intertemporal budget constraint A5. The maximization problem of the representative household A6. The consumption level of the representative household Appendix B References Contents 3 4 9 11 12 13 13 15 15 16 18 18 19 21 Designed for high-achieving graduates across all disciplines, London Business School’s Masters in Management provides specific and tangible foundations for a successful career in business. This 12-month, full-time programme is a business qualification with impact. In 2010, our MiM employment rate was 95% within 3 months of graduation*; the majority of graduates choosing to work in consulting or financial services. As well as a renowned qualification from a world-class business school, you also gain access to the School’s network of more than 34,000 global alumni – a community that offers support and opportunities throughout your career. For more information visit www.london.edu/mm, email mim@london.edu or give us a call on +44 (0)20 7000 7573. Masters in Management The next step for top-performing graduates * Figures taken from London Business School’s Masters in Management 2010 employment report Download free ebooks at bookboon.com Neoclassical Growth Model and Ricardian Equivalence 3 This note presents the neoclassical growth model in discrete time. The model is based on microfoundations, which means that the objectives of the economic agents are formulated explicitly, and that their behavior is derived by assuming that they always try to achieve their objectives as well as they can: employment and investment decisions by the firms are derived by assuming that firms maxi- mize profits; consumption and saving decisions by the households are derived by assuming that households maximize their utility.1 The model was first developed by Frank Ramsey (Ramsey, 1928). However, while Ramsey’s model is in continuous time, the model in this article is presented in discrete time.2 Furthermore, we do not consider population growth, to keep the presentation as simple as possible. The set-up of the model is given in section 2. Section 3 derives the model’s steady state. The model is then used in section 4 to illustrate Ricardian equivalence. Ricardian equivalence is the phenomenon that - given certain assumptions - it turns out to be irrelevant whether the government finances its expenditures by issuing public debt or by raising taxes. Section 5 concludes. Introduction 1. Introduction Download free ebooks at bookboon.com Neoclassical Growth Model and Ricardian Equivalence 4 The representative firm Assume that the production side of the economy is represented by a representative firm, which produces output according to a Cobb-Douglas production function: Yt = Kαt (AtLt) 1−α with 0 < α < 1 (1) Y is aggregate output, K is the aggregate capital stock, L is aggregate labor supply, A is the technology parameter, and the subscript t denotes the time period. The technology parameter A grows at the rate of technological progress g. Labor becomes therefore ever more effective.3 The aggregate capital stock depends on aggregate investment I and the depreci- ation rate δ: Kt+1 = (1− δ)Kt + It with 0 ≤ δ ≤ 1 (2) The goods market always clears, such that the firm always sells its total pro- duction. Yt is therefore also equal to the firm’s real revenues in period t. The dividends which the firm pays to its shareholders in period t, Dt, are equal to the firm’s revenues in period t minus its wage expenditures wtLt and investment It: Dt = Yt − wtLt − It (3) where wt is the real wage in period t. The value of the firm in period t, Vt, is then equal to the present discounted value of the firm’s current and future dividends: Vt = ∞∑ s=t ⎛ ⎝ s∏ s′=t+1 1 1 + rs′ ⎞ ⎠Ds (4) where rs′ is the real rate of return in period s′. The neoclassical growth model 2. The neoclassical growth model Download free ebooks at bookboon.com Pl ea se c lic k th e ad ve rt Neoclassical Growth Model and Ricardian Equivalence 5 Taking current and future factor prices as given, the firm hires labor and invests in its capital stock to maximize its current value Vt. This leads to the following first-order-conditions:4 (1− α)Yt Lt = wt (5) α Yt+1 Kt+1 = rt+1 + δ (6) Or in words: the firm hires labor until the marginal product of labor is equal to the marginal cost of labor (which is the real wage w); and the firm invests in its capital stock until the marginal product of capital is equal to the marginal cost of capital (which is the real rate of return r plus the depreciation rate δ). Now substitute the first-order conditions (5) and (6) and the law of motion (2) in the dividend expression (3), and then substitute the resulting equation in the value function (4). This yields the value of the representative firm in the beginning of period t as a function of the initial capital stock and the real rate of return:5 Vt = Kt(1 + rt) (7) The neoclassical growth model © Agilent Technologies, Inc. 2012 u.s. 1-800-829-4444 canada: 1-877-894-4414 Teach with the Best. Learn with the Best. Agilent offers a wide variety of affordable, industry-leading electronic test equipment as well as knowledge-rich, on-line resources —for professors and students. We have 100’s of comprehensive web-based teaching tools, lab experiments, application notes, brochures, DVDs/ CDs, posters, and more. See what Agilent can do for you.www.agilent.com/find/EDUstudents www.agilent.com/find/EDUeducators Download free ebooks at bookboon.com Neoclassical Growth Model and Ricardian Equivalence 6 The government Every period s, the government has to finance its outstan- ding public debt Bs, the interest payments on its debt, Bsrs, and government spending Gs. The government can do this by issuing public debt or by raising taxes Ts.6 Its dynamic budget constraint is therefore given by: Bs+1 = Bs(1 + rs) + Gs − Ts (8) where Bs+1 is the public debt issued in period s (and therefore outstanding in period s + 1). It is natural to require that the government’s public debt (or public wealth, if its debt is negative) does not explode over time and become ever larger and larger relative to the size of the economy. Under plausible assumptions, this implies that over an infinitely long horizon the present discounted value of public debt must be zero: lim s→∞ ( s∏ s′=t 1 1 + rs′ ) Bs+1 = 0 (9) This equation is called the transversality condition. Combining this transversa- lity condition with the dynamic budget constraint (8) leads to the government’s intertemporal budget constraint:7 Bt+1 = ∞∑ s=t+1 ⎛ ⎝ s∏ s′=t+1 1 1 + rs′ ⎞ ⎠Ts − ∞∑ s=t+1 ⎛ ⎝ s∏ s′=t+1 1 1 + rs′ ⎞ ⎠Gs (10) Or in words: the public debt issued in period t (and thus outstanding in period t+1) must be equal to the present discounted value of future tax revenues minus the present discounted value of future government spending. Or also: the public debt issued in period t must be equal to the present discounted value of future primary surpluses. The representative household Assume that the households in the economy can be represented by a representive household, who derives utility from her current and future consumption: Ut = ∞∑ s=t ( 1 1 + ρ )s−t lnCs with ρ > 0 (11) The parameter ρ is called the subjective discount rate. Every period s, the household starts off with her assets Xs and receives interest payments Xsrs. She also supplies L units of labor to the representative firm, and The neoclassical growth model Download free ebooks at bookboon.com Neoclassical Growth Model and Ricardian Equivalence 7 therefore receives labor income wsL. Tax payments are lump-sum and amount to Ts. She then decides how much she consumes, and how much assets she will hold in her portfolio until period s + 1. This leads to her dynamic budget constraint: Xs+1 = Xs(1 + rs) + wsL− Ts − Cs (12) Just as in the case of the government, it is again natural to require that the household’s financial wealth (or debt, if her financial wealth is negative) does not explode over time and become ever larger and larger relative to the size of the economy. Under plausible assumptions, this implies that over an infinitely long horizon the present discounted value of the household’s assets must be zero: lim s→∞ ( s∏ s′=t 1 1 + rs′ ) Xs+1 = 0 (13) Combining this transversality condition with her dynamic budget constraint (12) leads to the household’s intertemporal budget constraint:8 ∞∑ s=t ⎛ ⎝ s∏ s′=t+1 1 1 + rs′ ⎞ ⎠Cs = Xt(1 + rt) + ∞∑ s=t ⎛ ⎝ s∏ s′=t+1 1 1 + rs′ ⎞ ⎠wsL − ∞∑ s=t ⎛ ⎝ s∏ s′=t+1 1 1 + rs′ ⎞ ⎠Ts (14) Or in words: the present discounted value in period t of her current and future consumption must be equal to the value of her assets in period t (including interest payments) plus the present discounted value of current and future labor income minus the present discounted value of current and future tax payments. The household takes Xt and the current and future values of r, w, and T as given, and chooses her consumption path to maximize her utility (11) subject to her intertemporal budget constraint (14). This leads to the following first-order condition (which is called the Euler equation): Cs+1 = 1 + rs+1 1 + ρ Cs (15) Combining with the intertemporal budget constraint leads then to the current value of her consumption: Ct = ρ 1 + ρ ⎧⎨ ⎩Xt(1 + rt) + ∞∑ s=t ⎛ ⎝ s∏ s′=t+1 1 1 + rs′ ⎞ ⎠wsL− ∞∑ s=t ⎛ ⎝ s∏ s′=t+1 1 1 + rs′ ⎞ ⎠Ts ⎫⎬ ⎭ (16) The neoclassical growth model Download free ebooks at bookboon.com Pl ea se c lic k th e ad ve rt Neoclassical Growth Model and Ricardian Equivalence 8 Equilibrium Every period, the factor markets clear. For the labor market, we already implicitly assumed this by using the same notation (L) for the represen- tative household’s labor supply and the representative firm’s labor demand. Equilibrium in the capital market requires that the representative household holds all the shares of the representative firm and the outstanding government bonds. The value of the representative firm in the beginning of period t+1 is Vt+1, such that the total value of the shares which the household can buy at the end of period t is given by Vt+1/(1 + rt+1). The value of the government bonds which the household can buy at the end of period t is equal to the total public debt issued in period t, which is denoted by Bt+1. This implies that Xt+1 = Vt+1 1 + rt+1 + Bt+1 (17) Equilibrium in the goods market requires that the total production is consumed, invested or purchased by the government, such that Yt = Ct + It +Gt. Note that equilibrium in the goods market is automatic if the labor and the capital markets are also in equilibrium (because of Walras’ law). The neoclassical growth model Or in words: every period t, the household consumes a fraction ρ/(1 + ρ) of her total wealth, which consists of her financial wealth Xt(1 + rt) and her human wealth (i.e. the present discounted value of her current and future labor income), minus the present discounted value of all her current and future tax obligations.9 © U B S 20 10 . A ll ri g h ts r es er ve d . www.ubs.com/graduates Looking for a career where your ideas could really make a difference? UBS’s Graduate Programme and internships are a chance for you to experience for yourself what it’s like to be part of a global team that rewards your input and believes in succeeding together. Wherever you are in your academic career, make your future a part of ours by visiting www.ubs.com/graduates. You’re full of energy and ideas. And that’s just what we are looking for. Download free ebooks at bookboon.com Neoclassical Growth Model and Ricardian Equivalence 9 It is often useful to analyse how the economy behaves in steady state. To derive the steady state, we need to impose some restrictions on the time path of govern- ment spending. Let us therefore assume that government spending G grows at the rate of technological progress g: Gs+1 = Gs(1 + g) (18) To derive the steady state, we start from an educated guess: let us suppose that in the steady state consumption also grows at the rate of technological progress g. We can then derive the values of the other variables, and verify that the model can indeed be solved (such that our educated guess turns out to be correct). The steady state values of output, capital, investment, consumption, the real wage and the real interest rate are then given by the following expressions:10 Y ∗t = ( α r∗ + δ ) α 1−α AtL (19) K∗t = ( α r∗ + δ ) 1 1−α AtL (20) I∗t = (g + δ) ( α r∗ + δ ) 1 1−α AtL (21) C∗t = [ 1− α g + δ r∗ + δ ]( α r∗ + δ ) α 1−α AtL−G∗t (22) w∗t = (1− α) ( α r∗ + δ ) α 1−α At (23) r∗ = (1 + ρ)(1 + g) − 1 (24) ...where a superscript ∗ shows that the variables are evaluated in the steady state. Recall that the technology parameter A and government spending G grow at rate g while labor supply L remains constant over time. It then follows from the equations above that the steady state values of aggregate output Y ∗, the aggregate capital stock K∗, aggregate investment I∗, aggregate consumption C∗ and the real wage w∗ all grow at the rate of technological progress g. The steady state 3. The steady state Download free ebooks at bookboon.com Pl ea se c lic k th e ad ve rt Neoclassical Growth Model and Ricardian Equivalence 10 We can now draw two conclusions: First, suppose that the government increases government spending G∗t and after- wards continues to have G∗ growing over time at rate g (such that government spending is permanently higher). It then follows from equations (19) until (24) that aggregate consumption decreases one-for-one with the higher government spending. The rest of the economy, however, is not affected: aggregate output, the capital stock, investment, the real wage and the real interest rate do not change as a result of a permanent shock in government spending. So government spending crowds out consumption. Second, the way how the government finances its spending turns out to be ir- relevant for the behavior of the economy: whether the government finances its spending by raising taxes or by issuing public debt, does not matter. This phe- nomenon is called Ricardian equivalence. Ricardian equivalence actually holds not only in steady state, but also outside steady state. In the next section, we explore the reason for Ricardian equivalence in more detail. The steady state © Deloitte & Touche LLP and affiliated entities. 360° thinking. Discover the truth at www.deloitte.ca/careers © Deloitte & Touche LLP and affiliated entities. 360° thinking. Discover the truth at www.deloitte.ca/careers © Deloitte & Touche LLP and affiliated entities. 360° thinking. Discover the truth at www.deloitte.ca/careers © Deloitte & Touche LLP and affiliated entities. 360° thinking. Discover the truth at www.deloitte.ca/careers Download free ebooks at bookboon.com Neoclassical Growth Model and Ricardian Equivalence 11 Let us consider again the intertemporal budget constraint of the representative household, equation (14). Recall that the household’s assets consist of the shares of the representative firm and the public debt, such that Xt = Vt/(1 + rt) + Bt. Substituting in (14) yields: ∞∑ s=t ⎛ ⎝ s∏ s′=t+1 1 1 + rs′ ⎞ ⎠Cs = Vt + Bt(1 + rt) + ∞∑ s=t ⎛ ⎝ s∏ s′=t+1 1 1 + rs′ ⎞ ⎠wsL − ∞∑ s=t ⎛ ⎝ s∏ s′=t+1 1 1 + rs′ ⎞ ⎠Ts (25) Now replace Bt by the right-hand-side of the government’s budget constraint (equation (10), but moved backwards with one period): ∞∑ s=t ⎛ ⎝ s∏ s′=t+1 1 1 + rs′ ⎞ ⎠Cs = Vt + ∞∑ s=t ⎛ ⎝ s∏ s′=t+1 1 1 + rs′ ⎞ ⎠Ts − ∞∑ s=t ⎛ ⎝ s∏ s′=t+1 1 1 + rs′ ⎞ ⎠Gs + ∞∑ s=t ⎛ ⎝ s∏ s′=t+1 1 1 + rs′ ⎞ ⎠wsL− ∞∑ s=t ⎛ ⎝ s∏ s′=t+1 1 1 + rs′ ⎞ ⎠Ts (26) The present discounted value of tax payments then cancels out, such that the household’s intertemporal budget constraint becomes: ∞∑ s=t ⎛ ⎝ s∏ s′=t+1 1 1 + rs′ ⎞ ⎠Cs = Vt + ∞∑ s=t ⎛ ⎝ s∏ s′=t+1 1 1 + rs′ ⎞ ⎠wsL− ∞∑ s=t ⎛ ⎝ s∏ s′=t+1 1 1 + rs′ ⎞ ⎠Gs (27) This is a crucial result. It means that from the household’s point of view, only the present discounted value of government spending matters. The precise time path of tax payments and the size of the public debt are irrelevant. The reason for this is that every increase in public debt must sooner or later be matched by an increase in taxes. Households therefore do not consider their government bonds as net wealth, because they realize that sooner or later they will have to pay taxes to the government such that the government can retire the bonds. From the household’s point of view, it is therefore irrelevant whether the government has a large public debt or not: in the first case, households will have a lot of assets, but expect to pay a lot of taxes later on; in the second case, households will have fewer assets, but feel compensated for that as they also anticipate lower taxes. Ricardian equivalence 4. Ricardian equivalence Download free ebooks at bookboon.com Neoclassical Growth Model and Ricardian Equivalence 12 This note presented the neoclassical growth model, and solved for the steady state. In the neoclassical growth model, it is irrelevant whether the government finances its expenditures by issuing debt or by raising taxes. This phenomenon is called Ricardian Equivalence. Of course, the real world is very different from the neoclassical growth model. Consequently, there are many reasons why Ricardian Equivalence may not hold in reality. But nevertheless, the neoclassical growth model is a useful starting point for more complicated dynamic general equilibrium models, and the principle of Ricardian Equivalence often serves as a benchmark to evaluate the effect of government debt in more realistic settings. 1 Note that the Solow growth model (Solow, 1956) is sometimes called the neoclassical growth model as well. But the Solow model is not based on microfoundations, as it assumes an exogenous saving rate. 2 The stochastic growth model, which is at the heart of modern macroeconomic research, is in essence a stochastic version of the neoclassical growth model, and is usually presented in discrete time as well. 3 This type of technological progress is called labor-augmenting or Harrod-neutral techno- logical progress. 4 See appendix A for derivations. 5 See appendix A for a derivation. 6 In general, there is a third source of revenue for the government, namely seigniorage income. For simplicity, we make abstraction from this, and assume that seigniorage income is zero. 7 See appendix A for derivations. 8 The derivation is similar as for the government’s intertemporal budget constraint, and is given in appendix A. 9 Derivations of equations (15) and (16) are given in appendix A. 10 Derivations are given in appendix B. Conclusions 5. Conclusions Download free ebooks at bookboon.com Pl ea se c lic k th e ad ve rt Neoclassical Growth Model and Ricardian Equivalence 13 The maximization problem of the firm can be rewritten as: Vt(Kt) = max{Lt,It} { Yt − wtLt − It + 11 + rt+1 Vt+1(Kt+1) } (A.1) s.t. Yt = Kαt (AtLt) 1−α Kt+1 = (1− δ)Kt + It The first-order conditions for Lt, respectively It, are: (1− α)Kαt A1−αt L−αt − wt = 0 (A.2) −1 + 1 1 + rt+1 ∂Vt+1(Kt+1) ∂Kt+1 = 0 (A.3) In addition,