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An estimated dynamic stochastic general equilibrium model of the ...

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where β = 1/(1−τ+ r k ) . The current value <strong>of</strong> <strong>the</strong> capital stock depends negatively on <strong>the</strong> ex-antereal interest rate, and positively on its expected future value and <strong>the</strong> expected rental rate. TheQintroduction <strong>of</strong> a shock to <strong>the</strong> required rate <strong>of</strong> return on equity investment, η t , is meant as ashortcut to capture changes in <strong>the</strong> cost <strong>of</strong> capital that may be due to <strong>stochastic</strong> variations in <strong>the</strong>external finance premium. 16 We assume that this equity premium shock follows an IID-Normalprocess. In a fully-fledged <strong>model</strong>, <strong>the</strong> production <strong>of</strong> capital goods and <strong>the</strong> associated investmentprocess could be <strong>model</strong>led in a separate sector. In such a case, imperfect information between <strong>the</strong>capital producing borrowers and <strong>the</strong> financial intermediaries could give rise to a <strong>stochastic</strong> externalfinance premium. For example, in Bernanke, Gertler and Gilchrist (1998), <strong>the</strong> deviation from <strong>the</strong>perfect capital market assumptions generates deviations between <strong>the</strong> return on financial assets andequity that are related to <strong>the</strong> net worth position <strong>of</strong> <strong>the</strong> firms in <strong>the</strong>ir <strong>model</strong>. Here, we implicitlyassume that <strong>the</strong> deviation between <strong>the</strong> two returns can be captured by a <strong>stochastic</strong> shock, whereas<strong>the</strong> steady-state distortion due to such informational frictions is zero. 17The capital accumulation equation is standard:(31) Kˆ(1 ) ˆ ˆt = − τ Kt− 1 + τIt−1With partial indexation, <strong>the</strong> inflation equation becomes a more <strong>general</strong> specification <strong>of</strong> <strong>the</strong> standardnew-Keynesian Phillips curve:(32)βpˆ t = Etπˆt+1+ πˆt−11+βγ p 1+βγ pπ11+βγp(1 − βξpξ)(1 −ξpγp)+ka p[ αrˆt + (1 −α)wˆt − εˆt + η ]Inflation depends on past and expected future inflation and <strong>the</strong> current marginal cost, which itself isa function <strong>of</strong> <strong>the</strong> rental rate on capital, <strong>the</strong> real wage and <strong>the</strong> productivity parameter. When γ p = 0 ,this equation reverts to <strong>the</strong> standard purely forward-looking Phillips curve. In o<strong>the</strong>r words, <strong>the</strong>degree <strong>of</strong> indexation determines how backward looking <strong>the</strong> inflation process is. The elasticity <strong>of</strong>inflation with respect to changes in <strong>the</strong> marginal cost depends mainly on <strong>the</strong> degree <strong>of</strong> pricestickiness. When all prices are flexible ( ξ p = 0) and <strong>the</strong> price-mark-up shock is zero, this equationreduces to <strong>the</strong> normal condition that in a flexible price economy <strong>the</strong> real marginal cost should equalone.Similarly, partial indexation <strong>of</strong> nominal wages results in <strong>the</strong> following real wage equation:t1617This is <strong>the</strong> only shock that is not directly related to <strong>the</strong> structure <strong>of</strong> <strong>the</strong> economy.This shock can also take up exogenous distortions or non-rational bubbles in asset prices. For such alternativeinterpretations <strong>of</strong> this equity premium shock and an analysis <strong>of</strong> optimal monetary policy in <strong>the</strong> presence <strong>of</strong> suchshocks, see Dupor (2001).12 NBB WORKING PAPER No.35 - October 2002

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