board independence has been regarded as one of the important determinants of the ability of boards to protect investors interests.However,using the proportion of inside and outside directors to represent board independence has produced varying results on firm's performance.Inside directors are those who hold dual positions as director and manager concurrently,whereas outside directors are non-executive or non-managerial directors and are also known as independent directors. Hermalin and Weisbach's summarization of empirical researches determined that board composition,based on insider-outsider ratio,dose not have any relationship with firm performance. Bhagat and Black ,Dalton et al.(1999),peng et al.(2003), Yoshikawa and Phan(2003),and Dahya and McConnell (2005) also found no evidence of boards dominated by outside directorship producing better outcomes than those dominated by inside directorship.