La contrazione della formazione di imprese dopo la crisi finanziaria del 2008 è stata in parte determinata dall'inasprimento degli standard creditizi. Incorporare l'imperfezione del mercato del credito nei modelli DSGE è diventato un passo essenziale verso una migliore spiegazione di tali risultati. Nel primo capitolo, indago sul ruolo del finanziamento esterno nella creazione d'impresa. Sottolineo l'impatto del potere di mercato delle banche e la presenza di dispersione tra i tassi di interesse dei grandi e dei piccoli prestiti all'ingresso. Pertanto, sviluppo un modello DSGE che collega l'ingresso dell'impresa al sistema bancario imperfetto e introduco costi di prestito eterogenei per operatori storici e nuovi. Il modello prevede un impatto amplificato degli shock reali e finanziari e mostra una maggiore volatilità man mano che lo spread dei tassi di interesse si allarga. In linea con l'evidenza, la versione sticky-price produce un'entrata prociclica in risposta allo shock monetario espansivo. Nel secondo capitolo, mi concentro sull'interazione tra i prezzi delle case, le insolvenze sui prestiti e l'ingresso di imprese. Presento prove SVAR che rivelano una risposta prociclica positiva della nascita allo shock dei prezzi delle case e una reazione negativa alle inadempienze sui prestiti. Quindi sviluppo un modello DSGE in grado di prevedere e spiegare queste risposte. L'endogeneità del vincolo collaterale e della creazione d'impresa è al centro del meccanismo del modello. Il modello genera dei secondi momenti ragionevolmente vicini alle controparti dei dati. / The contraction of business formation after 2008 financial crisis was driven partly by the tightened credit standards. Incorporating credit market imperfection to DSGE models became an essential step towards better explaining such outcomes. In the first chapter, I investigate the role of external financing in firm creation. I highlight the impact of bank market power, and the presence of dispersion between interest rates of large and small loans on entry. Therefore, I develop a DSGE model linking firm entry to imperfect banking system, and introduce heterogeneous borrowing costs for incumbents and entrants. The model predicts amplified impact of real and financial shocks, and exhibits higher volatility as the spread in interest rates gets wider. In line with evidence, the sticky-price version produces pro-cyclical entry in response to expansionary monetary shock. In the second chapter, I focus on the interaction between house prices, loan defaults, and firm entry. I present SVAR evidence that reveals positive pro-cyclical response of birth to house price shock, and negative reaction to loan defaults. Then I develop a DSGE model that is able to predict and explain these responses. The endogeneity of collateral constraint and firm creation is in the core of the model’s mechanism. The model generates some second moments that are reasonably close to their data counterparts.

本文的研究目的為，在一個含有房屋及房屋相關貸款的動態隨機一般均衡模型的架構中，比較貨幣政策、財政政策以及總體審慎政策對於房屋價格及房屋相關貸款的穩定效果。本文建構一個經濟封閉體系，其中包含三種不同家計單位、商品生產部門、房屋建商、資本生產部門，並且由政府部門制定相關政策；此模型的特色為，不同家計單位中的借貸行為、名目價格僵固性以及透過房屋價格抵押貸款的限制來刻劃金融摩擦。我們考慮了一般緊縮貨幣政策、提高財產稅率以及緊縮貸款價值比；本文發現，在三種政策中，對於抑制房屋價格以及降低住房貸款對國內生產毛額的比例，財政政策及總體審慎政策比起緊縮貨幣政策擁有較好的效果。 / The main purpose in this paper is to compare the effect of monetary policy, fiscal policy and macroprudential policy on housing price and housing related loans using a micro-based dynamic stochastic general equilibrium (DSGE) model with housing and housing related loans. We equip a closed economy model with three types of infinitely-lived households (patient households, impatient households and renters), a goods firm, housing and capital producer and a government sector. The model features borrowing and lending between patient and impatient households, nominal rigidity in goods price and financial friction in the form of collateral constraints tied to price of house. We consider the contractionary monetary policy by raising the interest rate, fiscal policy by increasing property tax rate and the macroprudential policy through tightening the loan-to-value (LTV) ratio. We find that among these three policies, in terms of dampening the price of housing and lowering the loan-to-GDP ratio, raising the property tax and lowering the LTV ratio outperforms the contractionary monetary policy.

本研究建構一社會網路互動下的新凱因斯動態隨機一般均衡模型，探討效用基礎下波茲曼分配背後的網路結構，以及，社會網路對新凱因斯動態隨機一般均衡模型參數的影響。根據本論文模擬結果，效用基礎下波茲曼分配背後所隱含的社會網路結構呈現局部區域性連結拓璞，此結論與熱力學對波茲曼分配中粒子互動方式的假設相同，然而，區域性連結之網路結構（如環狀網）並非目前實證研究所觀察到的網路型態（如冪分布網路或高群集係數之小世界網路），故吾人是否得以直接利用效用基礎下波茲曼分配來描述社會上人與人之間的互動現象必需更忱慎考量之。另外，社會網路互動也將使新凱因斯動態隨機一般均衡模型之參數估計產生偏誤，依本研究估計結果觀之，只要加入社會互動，總合需求曲線中實質利率之參數估計將為正號，即實質利率對產出缺口的影響為負向影響，也就是文獻上的投資儲蓄迷思(IS puzzle)，若進一步觀察社會網路結構對該實證迷思的影響則可發現當社會網路群聚程度越高時，該估計偏誤將越嚴重。 / We construct a social network-based New Keynesian DSGE (Dynamic Stochastic General Equilibrium) Model to investigate the underlying social network structure derived from the performance-based Boltzmann-Gibbs model, and thus interpret the process that social network structures affect the estimation bias in the New Keynesian DSGE framework. According to our simulation results, the underlying social network structure derived from the performance-based Boltzmann-Gibbs model should be local. This finding is consistent with the study of thermodynamics, which the Boltzmann-Gibbs distribution is based upon, i.e. the local interaction. However, it contradicts not only the purpose of combining the performance-based Boltzmann-Gibbs machine and New Keynesian DSGE model, but also empirical studies of social network structures in the real world. Accordingly, maybe we have to consider further whether the performance-based Boltzmann-Gibbs machine is a suitable tool for calibrating social interaction under the stylized New Keynesian DSGE framework. Furthermore, if we embedded interaction behavior in the stylized New Keynesian model, the so-called “IS Puzzle” can be consequently observed. We also realized that “IS Puzzle” is connected with network structures. The more clustering the network structure is, the more significant “IS Puzzle” would be.

本文建構代理人基之社會網路新凱因動態隨機一般均衡模型(Social Network-Based DSGE model)，並分別使用權衡性門檻型泰勒法則與一般線型泰勒法則作為代理人基之社會網路新凱因斯動態一般均衡模型中的貨幣政策方程式，模擬產出缺口、通貨膨脹、利率等總體經濟變數資料，接著利用模擬資料，探討不同網路結構對產出缺口、通貨膨脹等總體經濟變數的影響，同時比較權衡性貨幣政策與法則性貨幣政策穩定經濟的有效性。 　　透過產出缺口與通貨膨脹的波動性分析，本研究發現某些特定社會網路結構的影響力大於貨幣政策的影響力，決定了經濟變數的波動程度。在完全連結網路(Fully)的結構下，通貨膨脹與產出缺口的波動度明顯低於其他結構，而無標度網路(Scalefree)的結構會使產出與通膨的波動程度最大。經過驗證，本研究發現群聚度大、平均路徑短的網路結構內節點之間資訊流通速度較快，對穩定經濟有正面助益；相反的，由於無標度網路強大的中心性，使該網路內指標性節點對其餘節點具有龐大影響力，增加節點內決策的不確定性，連帶造成經濟的大幅波動。另外，在相同的網路結構下比較權衡與法則貨幣政策，研究結果指出權衡性政策會造成較大的產出缺口波動，但對抑制通貨膨脹波動的效果較佳；相對的，法則性政策對產出缺口的穩定效果較好，但卻無法兼顧通貨膨脹的波動性。 / We construct an agent-based New Keynesian DSGE model (Dynamic Stochastic General Equilibrium) with different social network structures to investigate the effects of the rule and discretion monetary policy. According to our simulation results, we find the economic stability depends on the specific social network structure rather than the monetary policy basis like rule and discretion. Generally speaking, the more average path length (the less average clustering coefficient) the network structure is, the more economic fluctuation would be. Also, the results show that scalefree network will lead the most dramatic economic fluctuations. These results are ascribed to scale -free’s high centrality. However, if the social network structure is too complicate to control, the central banker can only manipulate the monetary policy to stabilize the economy. With different policy basis, we find the rule monetary policy will lead less output gap volatility.

本文的研究目的為，在一個包含銀行部門的動態隨機一般均衡模型的架構中，探討流動性覆蓋比率限制在利率的信用管道中所扮演的角色以及其對政體經濟的影響為何。在銀行的資產配置決策內生的情形下，加入流動性覆蓋比率的限制，透過放款的勞動成本與抵押品價值來刻畫金融摩擦；本文發現當經濟體系遭受生產與放款的外生衝擊時，流動性覆蓋比率的限制會增強政策利率的信用管道效果，並且相較於無流動性覆蓋比率限制之模型而言，具流動性覆蓋比率限制的模型，其銀行資產配置的變動幅度與金融摩擦的程度皆較大。 / The main purpose of this paper is to explore the role of the liquidity coverage ratio (LCR) in the credit channel and how it influences the overall economy in a dynamic stochastic general equilibrium (DSGE) model with banking sector. Commercial banks endogenously choose their optimal portfolio of assets under the liquidity coverage ratio restriction. On the other hand, we describe the financial friction through the labor cost of making loans and collateral value. We find that when the economy is exposed to exogenous shocks in production and lending, the liquidity coverage ratio will enhance the effect of credit channel. Compared with the model with no LCR restriction, the degree of change of the bank asset allocation and the financial friction are larger in the model with LCR restriction.