The Effectiveness of Capital Requirement in Preventing against Bank Panic and Contagion Phenomenon

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