市場集中度對銀行效率之影響，一直是金融領域的重要議題。本研究以與台灣經貿緊密相連之東亞國家，包括中國、香港、日本、韓國及我國為研究對象，探討各國市場集中度是否影響銀行的效率？我們採用隨機邊界法(stochastic Frontier approach；SFA)，同時設定translog隨機成本邊界函數及無效率模型，探討市場集中度對銀行成本效率之影響。之後再根據前述估計結果，計算各國銀行之規模經濟與範疇經濟，據以分析市場集中度對規模經濟與範疇經濟的影響。實證結果發現，台灣、香港與中國銀行資產市占率的增加，會提升銀行成本效率。資產HHI值提高，除香港能使成本效率顯著改善外，其他國家則會降低銀行業成本效率。此外，台灣、日本之銀行多處於固定規模報酬階段；韓國、香港近年則有規模報酬遞增的趨勢；中國則處於規模報酬遞減的階段。最後，我們發現，台灣、日本與香港的 與HHI値皆未達最適規模報酬值，顯示市場集中度值上升，會使規模報酬遞增。東亞五國HHI變動對範疇經濟的影響皆為顯著。但變動對範疇經濟的影響僅台灣、日本、韓國、香港顯著。
How banks' concentration degree influences banks' earning is always an important academic issue in financial economics. Does a higher degree of banks' concentration lead a better performance of banks? We finds that the scale of Taiwan's and Japan's banks has been in the stage of constant returns to scale while the ones of Korea and Hong Kong have been in a trend to increasing returns to scale in recent years. However, China's banking has been in the stage of decreasing return to scale. Since all countries had the advantage of the scope of economy, they should try to diversify their banking business. Although all 5 East Asian countries face the increase of the degree of concentration in banking, there has no a uniform rule to show that market concentration raises or pulls down their bank's performance. Based on our empirical results of scale economies and economics of scope, the East Asian countries' financial authorities should regard those as the indicators to implement their policies.
