自1997亞洲金融風暴以來，區域性金融危機的傳染現象(Contagion, or Spillover Effect)便受到經濟學界高度重視，其重要性在2008年雷曼兄弟事件所引發的全球性金融海嘯後更加突顯，而相關的資本管制也陸續出籠，其中最引人注目的當屬2010年通過實行的三代巴賽爾條約(Basel III)。本文奠基於Allen and Gale(2000)所提出的銀行同業拆借市場(Interbank Market)模型，配合資本適足率的導入，試圖驗證在資本管制的設定之下，是否能有效預防銀行恐慌與其蔓延現象之發生。其結果證實提高資本適足率後，藉由銀行本身主動的提高緩衝性準備(Buffer)，銀行倒閉的發生機率將顯著降低，換言之，資本適足率管制有效提高了銀行倒閉門檻。同時，本文亦證實資本管制對於銀行同業拆借市場所衍生的傳染現象具有顯著的改善效果。 然而，資本適足率之管制雖具有穩定金融體系的作用，其對存款人消費之緊縮效果卻無可避免會降低其效用。本文在考慮銀行倒閉風險機率後，建立一兩期之社會福利涵數，並利用計算代表性個人(Representative Agent)預期效用極大化條件下的最適資本適足率。在特定參數之下，所得到最適資本適足率為6.375%。我們並且進一步證實，在權益資金報酬率小於長期資產報酬率之下，最適之資本適足率將同步增加，進而使社會福利最大，此符合一般的經濟直覺，同時再次突顯金融體系穩定性對於社會福利的重要性。 / The financial contagion phenomenon, or the spillover effect, has become a crucial issue in recent years after the breakout of the financial crises in 2008. To deal with such problem, some regulations such as the capital requirement, has been introduced as a solution. In our paper, we develop a model based on Allen and Gale (2000) to testify whether the introduction of the capital requirement can successfully reduce the risks of bankruptcy and contagion phenomenon for the interbank system when suffering from the regional liquidity shock. We conclude that after the introduction of capital requirement, the bank will voluntarily hold more buffers to lower the bankruptcy risk and reduce the spillover effect. What’s more, we construct an optimal level of the capital requirement that maximize the social welfare utility and depends on the probability of bankruptcy, the percentage of early withdrawals, the relative cost of capital and other parameters. By simulation, we have the optimal capital requirement at 6.375% in our benchmark case, which is a reasonable one compared with the current Basel Accord. Finally, the paper shows that as the cost of capital is getting lower, bank uses more capital which enhances the social welfare significantly in equilibrium, indicating the great importance of financial stability.

本研究旨在說明資本適足率對於銀行業資訊傳遞效果之影響，利用Allen and Gale (2000)模型討論在不完整市場結構下，銀行間因為持有銀行同業存款而形成相連的傳染途徑，進而影響整個系統，本研究擴展Allen and Gale (2000)的模型，加入資本適足率的考量，從而進一步探討透過資本適足要求能否有效提高銀行整體穩定性。 模型假設因為不同區域對於早、晚期消費需求不同，可藉由區域間的資源移轉，來達到最適分配情況。隨著資本適足率的納入，將改變最適分配解，同時分析緩衝(buffer)、擴散效果(spillover effect)及傳染(contagion)的變化。文中傳染定義為擴散效果扣除緩衝力道的淨結果，並說明若有超額流動性消費需求衝擊時，一家銀行的倒閉將如何傳染至整個銀行體系。 此研究發現，在資本適足規定下，若長期資產報酬率越大，會更有機會取得較大的緩衝能力，但將面對較大的擴散效果。關於傳染現象，則是發覺當銀行同業存款越小，在資本適足規定下的傳染機會越低；若長期資產的早期報酬率越大，同樣可降低發生傳染現象機率，即驗證資本適足率對於銀行穩定性的貢獻。 / The objective of this study is to testify the effect of capital requirement with regard to information transmission among banks. We develop a model based on Allen and Gale (2000) to discuss that under incomplete market structure, contagion channel is built because of interbank deposits market. We also expand Allen and Gale’s model by putting new parameter, capital requirement, into this model to analyze the impact of capital requirement with respect to stability in banking system. Due to different liquidity demands at each date in different regions, banks can exchange resources in the system to reach the first-best allocation. With capital requirement, the first-best allocation varies and so does buffer, spillover effect and contagion. In this article, contagion is defined as the net result of spillover effect minus buffer. Besides, we explain how the bankruptcy in one region evolves into the bankruptcy in the whole system under excess demand for liquidity. We find out that with capital requirement, if return of long-term asset at final date is higher, there will be more chances to have more buffers but larger spillover effect. As for contagion, it shows that with lower interbank deposits or higher return of long-term asset at early date, the possibility of contagion will be reduced. As a result, we can conclude that capital requirement really improves the stability in banking system.