本研究旨在探討會計師之客戶集中度與審計品質之關聯性，並進一步檢視客戶之集中程度對審計品質之影響在客戶所屬產業多樣性不同的情況下是否存在差異。本研究預期客戶集中度較高之會計師在面臨資源有限的狀況，會將有限的審計資源、人力與時間優先分配給對會計師較具影響力之客戶，即獲利來源比重較高之客戶，而剩餘資源再給影響力相對較小之客戶，造成資源分配不均的扭曲現象。此種客戶組成結構造成會計師在考慮審計失敗之可能與聲譽受損之風險下，會將查核重心挹注於主要客戶，而相對忽略非主要客戶，處使整體審計品質下降，換句話說客戶集中度越高，整體的審計品質會下降，而這情況在會計師所有客戶之產業類別越多樣時會更加明顯，因為各個產業都有不盡相同的產業特性，而在查核資源有限的情況下，會計師無法兼顧所有客戶的查核品質，同樣造成審計品質之下降。研究結果證實，客戶集中度越高，異常應計數越高，財務報表重編的機率也越高，皆代表客戶集中度與審計品質呈現負向相關，且皆達顯著水準。而客戶集中度與審計品質之負向關係在客戶產業越多樣時更加強烈。本研究結果提供會計師事務所在分配業務、財務報表外部使用者做決策及主管機關監督會計師執行審計業務時之參考。

The aim of this study is to examine the associations among auditor client concentrations, industry diversity, and audit quality. I further test whether the relationship between auditor client concentration and audit quality in terms of client industry diversity is different in the auditor’s portfolio. Faced with the situation of limited audit resources, such as time and human resources, an auditor with a more concentrated client base may over-allocate audit resources to the clients who generate higher revenues. It is also implied that such clients will in turn have more power in the auditor-client relationship. I hypothesize that this kind of resource distortion, making an auditor focus on important clients when there are limited resources rather than on their less important counterparts results in a negative association between client concentration and audit quality. Furthermore, if industry diversity among an auditor’s clients affects this negative association, I used the performance-adjusted abnormal accruals and restatement as proxies of audit quality. I find a negative association between client concentration and audit quality, and this relation is more pronounced for when there are more different industries in an auditor’s client portfolio.

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