萨尔瓦多的《国际经济学基础》ppt(dominick salvatore).ppt

13 - * Income determination in a closed economy This yields an equilibrium condition of: S – I = 0. In words, this entails that at equilibrium leakages from the economy (S) must be balanced by injections into the economy (I). 13 - * Income determination in a closed economy In words, this entails that at equilibrium leakages from the economy (S) must be balanced by injections into the economy (I). If planned investment is autonomous but savings is determined by the marginal propensity to save (s), then: ΔS = sΔY. The marginal propensity to save (s) is amount of additional savings that flows from each additional dollar of income. 13 - * Income determination in a closed economy If planned investment is autonomous but savings is determined by the marginal propensity to save (s), then: ΔS = sΔY. Since S = I at equilibrium, this entails that: ΔI = sΔY or 1 ÷ s = ΔY ÷ ΔI. 13 - * Income determination in a closed economy Since S = I at equilibrium, this entails that: ΔI = sΔY or 1 ÷ s = ΔY ÷ ΔI. If k = 1 ÷ s, then ΔY = k ? ΔI. k is the multiplier. Any change in investment will induce a multiplied change in income as given by the above formula. 13 - * Income determination in a closed economy If k = 1 ÷ s, then ΔY = k ? ΔI. An example s = 0.25 ΔI = 300 What is the value of k? k = 1 ÷ 0.25 = 4 What is the change in income? ΔY = 4 ? 300 = 1,200 13 - * Income determination in an open economy In an open economy, equilibrium is still determined by the condition that leakages must equal injections. In an open economy, imports (M) are a new leakage. In an open economy, exports (X) are a new injection. 13 - * Income determination in an open economy In an open economy, equilibrium is still determined by the condition that leakages must equal injections. The new equilibrium equation is: S + M = I + X or ΔS + ΔM = ΔI + ΔX. 13 - * Income determination in an open economy The new equilibrium equation is: S + M = I + X or ΔS + ΔM = ΔI + ΔX. If ΔM = mΔY, then the multiplier (k*) becomes: k*