傳統的審計文獻認同DeAngelo (1981b) 之觀點：會計師的客戶數與審計品質呈正相關。在知識經濟時代，「商業互補」已成為公司的重要策略，此策略是否導致會計師提高對查核公司之經濟依賴，降低其審計品質，因而改變會計師客戶數與審計品質之關係，是一個值得探討的問題。由於在相同供應鏈之公司，彼此具有商業互補關係，本研究探討在相同的供應鏈之下，會計師的客戶數與審計品質之間是否仍維持正相關。本研究以裁決性應計數衡量審計品質，發現會計師單查核一家公司的審計品質顯著高於同時查核公司與其供應商（或顧客）；換言之，當考慮商業互補之變數後，會計師的客戶數與審計品質呈顯著負相關。本研究進一步比較公司、供應商與顧客是否由同一會計師查核之審計品質差異，仍發現考慮商業互補的變數之後，DeAngelo (1981b)之觀點需要修正。 In previous auditing literatures, researchers agreed the argument posited by DeAngelo(1981b) that there was positive relationship between CPA’s number of clients in audit firm and audit quality. Increasing business complementarity has become an important strategy for companies in the knowledge-based economy. I postulate that business complementarity will decrease audit quality because CPA’s increased economic dependence upon its audited companies. Therefore, it needs to re-test DeAngelo’s(1981b) perspective. I investigate whether the positive relationship between the number of clients in audit firm and audit quality (measured by discretionary accruals) in a supply chain, which business complementarity may exists among companies, in this paper. I find that audit quality is higher significantly if CPA audited one company than audited both the audited company and its supplier (or customer). In other words, after considering business complementarity, I find that there is negative relationship between CPA’s client numbers and audit quality. Further, I test whether auditor’s audit quality will change if the company and its supplier and customer were audited by the same auditor or not. All of my results do not support DeAngelo’s(1981b) argument.
