The Association Between Audit Market Concentration and Audit Quality

安達信會計師事務所解體後引發各界持續關注審計市場集中度的上升。由於公開發行公司的審計市場呈現四大寡占的現況，本研究以2003年至2013年四大查核的公開發行公司為研究樣本，檢視審計市場集中度是否對審計品質有潛在負面影響。參考過去多數研究，本文以控制績效的異常應計數絕對值代理審計品質，至於市場集中度的衡量係分別採家數與營收基礎之市占率平方值合計。實證結果發現，四大審計市場集中度與異常應計數絕對值呈顯著正向關聯，代表四大審計市場集中度愈高，受查者盈餘管理幅度愈大，審計品質恐有損傷之疑慮；進一步分群檢視，發現台灣前三大會計師事務所之集中度指標均與異常應計數絕對值呈正向關聯，部分支持管制者對於審計市場集中度上升的疑慮。Rising audit market concentration has received ongoing concerns among regulators, market participants and academics especially following the Anderson's demise. Since audit market of public companies is characterized by an oligopoly of Big 4 audit firms, this study uses 2003 ~ 2013 public company audited by Big 4 audit firms as a sample to examine whether there is the potential negative impact of audit market concentration on audit quality. Following most prior studies, audit quality is surrogated by abnormal accruals which are based on a modified Jones model controlling for firm performance. Market concentration is calculated by summing up the square value of market share based on total client numbers and total client sales. Empirical results find that Big 4 audit market concentration is positively associated with absolute value of abnormal accruals, indicating that the higher the Big 4 concentration the larger the auditees' earnings management magnitude, impairing to the audit quality. Further analyses show that the positive association between concentration and absolute value of abnormal accrual exists in Taiwan's Big 3 subsamples. Overall, the evidence provides some support for concerns of regulators about the rising audit market concentration