La Domanda del settore privato: consumo e investimento Capitolo 6 La Domanda del settore privato: consumo e investimento

Variability of GDP Components, 1970-2001 Fig. 6.01 Variability of GDP Components, 1970-2001 Figure 6.1

Indifference curves: Normal case Fig. 6.02(a) Indifference curves: Normal case Consumption tomorrow Consumption today Figure 6.2(a)

Indifference curves: Zero substitution Fig. 6.02(b) Indifference curves: Zero substitution Consumption tomorrow Consumption today Figure 6.2(b)

Indifference curves: Constant substitution Fig. 6.02(c) Indifference curves: Constant substitution Consumption tomorrow Consumption today Figure 6.2(c)

Fig. 6.03 Optimal consumption Begin Figure 6.3

Optimal consumption: borrower Fig. 6.03 Optimal consumption: borrower IC3 B D IC2 IC1 (i) Consumption today financed on credit M Y1 Y2 (ii) (ii) Consumption loan repayment (including interest) Consumption tomorrow R C1 C2 -(1+r) Consumption today Figure 6.3(a)

Optimal consumption: lender Fig. 6.03 Optimal consumption: lender D (i) Saving from this period’s income Consumption tomorrow (ii) (ii) Additional consumption next period R C1 C2 Y2 A IC3 IC2 IC1 -(1+r) Y1 B Consumption today Figure 6.3(b)

Ciclo di vita del consumo Fig. 6.04 Ciclo di vita del consumo Figure 6.4

Consumo ottimale

La funzione di utilità sopra scritta si ottiene sostituendo al posto di C1 l’espressione del lucido precedente e trascurando  che è costante

Life-cycle consumption Fig. 6.04 Life-cycle consumption Income, Consumption Income Saving Consumption Permanent income Borrowing Time Figure 6.4

Variazioni permanenti e temporanee del reddito Fig. 6.05 Variazioni permanenti e temporanee del reddito Figure 6.5

Temporary income change Fig. 6.05 Temporary income change D´ B´ B D Consumption tomorrow R´ Y1 Y2 A=R A´ Y1´ Consumption today Figure 6.5

Permanent income change Fig. 6.05 Permanent income change D´ B´´ D A´´R´´ Consumption tomorrow Y2´ R´ Y2 A=R A´ Y1 Y1´ B B´ Consumption today Figure 6.5

Temporary vs. permanent income change Fig. 6.05 Temporary vs. permanent income change D´ Temporary: R to R´ Permanent: R to R´´ D A´´R´´ Consumption tomorrow Y2´ R´ Y2 A=R A´ Y1 Y1´ B B´ B´´ Consumption today Figure 6.5

Real GDP and retail sales growth: Czech Republic, 1997-2002 Fig. 6.06 Real GDP and retail sales growth: Czech Republic, 1997-2002 Figure 6.6

Real price of crude oil, 1956-2002 Fig. 6.07 Real price of crude oil, 1956-2002 Figure 6.7

Current accounts in three countries, 1956-2002 Fig. 6.08 Current accounts in three countries, 1956-2002 Figure 6.8

Gli effetti di un aumento del tasso di interesse Fig. 6.09 Gli effetti di un aumento del tasso di interesse Figure 6.9

Fig. 6.09 Recall: borrowers consume to the right of their endowment A, lenders to the left of A. B D B D A Consumption tomorrow Consumption tomorrow R R A Consumption today Consumption today (a) Student Crusoe (borrower) (b) Professional athlete (lender) Figure 6.9

Fig. 6.09 Effect of an increase in the interest rate: negative income effect for borrowers, positive for lenders B´ B´ D D A R´ Consumption tomorrow Consumption tomorrow R R R´ A B B Consumption today Consumption today (a) Student Crusoe (borrower) (b) Professional athlete (lender) Figure 6.9

Fig. 6.09 For borrowers: income and substitution effects work in the same direction (to increase saving) B´ B´ D D A R´ Consumption tomorrow Consumption tomorrow R R R´ A B B Consumption today Consumption today (a) Student Crusoe (borrower) (b) Professional athlete (lender) Figure 6.9

Fig. 6.09 For lenders: income and substitution effects work in opposite directions (below income effect wins) B´ B´ D D A R´ Consumption tomorrow Consumption tomorrow R R R´ A B B Consumption today Consumption today (a) Student Crusoe (borrower) (b) Professional athlete (lender) Figure 6.9

Consumption, wealth and disposable income: Fig. 6.10 Consumption, wealth and disposable income: France, 1980-2002 Fig. 6.10

Fig. 6.11 I vincoli al credito Figure 6.11

When the household is not credit constrained... Fig. 6.11 When the household is not credit constrained... C Consumption tomorrow A repay R borrow D Consumption today Figure 6.11

With a credit constraint, the choice set is reduced. Fig. 6.11 With a credit constraint, the choice set is reduced. C Consumption tomorrow A B R D Consumption today Figure 6.11

Funzione del consumo: C = C(, Yd)

Figure 6.12 GDP, domestic demand and the current account: Poland and East Germany Figure 6.12

Lo stock ottimale di capitale Fig. 6.13 Lo stock ottimale di capitale Figure 6.13

Fig. 6.13 R Output Output Optimal capital stock is larger than starting capital stock Capital stock Marginal productivity of capital MPK Marginal cost of capital We start with Capital stock Figure 6.13

Figure 6.13 MPK>1+r, so it is profitable to invest up to R MPK Output Output MPK>1+r, so it is profitable to invest up to Capital stock Marginal productivity of capital MPK Marginal cost of capital Capital stock Figure 6.13

Technological progress Fig. 6.14 Technological progress Figure 6.14

Figure 6.14 We will start with an optimal capital stock... R MPK Output Output Capital stock Marginal productivity of capital MPK Capital stock Figure 6.14

Marginal productivity of capital Fig. 6.14 MPK´ New R Output Output Old Technological progress makes more output possible with the same capital stock. Desired capital stock increases. Capital stock Marginal productivity of capital MPK Capital stock Figure 6.14

Funzione di investimento I è una qualche funzione della differenza tra K* e K corrente; dal momento che K è una funzione inversa di r, anche I dipenderà inversamente da r I = I(r)

Modello accelerativo K* = vY I1 = K2* – K1* = v(Y2 – Y1) = vY2 v? Y = AK  MPK = Y/K Y/K = 1 + r K* = Y/(1+r) v = /(1+r) 2 < v < 3 I1 = vY2 + K1

Modello della q di Tobin I prezzi delle azioni (PAZ) riflettono i profitti futuri Variazioni di PAZ sono una stima delle aspettative future dei profitti Tale stima dei profitti può differire dal prezzo dei beni capitali che costituiscono l’impresa, a volte definito costo di sostituzione di K

Q di Tobin = valore di mercato di K/valore di sostituzione di K I due valori possono differire per molti motivi, uno dato dai costi di aggiustamento Quando q>1 vuol dire che il valore di mercato di K è superiore al costo (complessivo, cioè con i costi di aggiustamento) per acquisire e avviare un’impresa.

The q-theory of investment Fig. 6.15 The q-theory of investment Investment Tobin’s q 1 Figure 6.15

Relazione tasso di interesse e q di Tobin +r  - PAZ  - q In generale, la q di Tobin sintetizza molte variabili; inoltre è rivolta al futuro; ruolo delle aspettative.

Investment and Tobin’s q: Inter-war Germany Fig. 6.16(a) Investment and Tobin’s q: Inter-war Germany Figure 6.16(a)

Investment and Tobin’s q: Modern Germany Fig. 6.16(b) Investment and Tobin’s q: Modern Germany Figure 6.16(b)

Q di Tobin con costi di aggiustamento K2=I1

K2 = I1+ (1-)K1

Definiamo ora la q di Tobin come

Allora possiamo riscrivere la condizione del 1 ordine come

Figure 6.17 Tobin’s q=1 in a world of no adjustment costs If there were no costs of adjustment, the present value of the marginal cost of capital would be independent of the investment rate. MPK1 Present value of MPK, cost of capital C 1 Note if there were no depreciation, the investment rate, I/K, = DK/K, the rate of change of the capital stock. Investment rate (I/K) (a) MPK=Marginal return of new investment Figure 6.17

Figure 6.17 Tobin’s q when adjustment costs are significant Marginal cost of investment However the faster we try to install new capital, the more it adds to the cost of that capital. “Haste makes waste.” Hence the upward slope of the marginal cost of investment with respect to the investment rate. MPK1 Present value of MPK, cost of capital A C 1 Investment rate (I/K) (a) MPK=Marginal return of new investment Figure 6.17

Fig. 6.17 Tobin’s q With the investment rate corresponding to the rate at point A, in the following period there will be more capital and a lower MPK. Marginal cost of investment Present value of MPK, cost of capital A MPK2 B The investment rate next period will fall too (as will Tobin’s q), ultimately heading toward a value of unity and no more investment. 1 MPK1 Investment rate (I/K) (b) MPK=Marginal return of new investment Figure 6.17