대규모기업집단의 주력회사는 지배구조 최상위에 있기 때문에 주력회사와 그 감사인은 주력회사와 계열회사 그리고 계열회사 상호간의 내부거래에 대하여 전반적인 정보를 파악하는 데 용이한 위치에 있다. 이러한 관점에서 주력회사의 감사인이 계열회사도 동시에 감사한다면 감사인은 위험이 높은 내부거래에 대하여 보다 높은 수준의 감사증거를 수집할 수 있기 때문에 계열회사의 감사품질이 높을 것으로 기대할 수 있다. 본 연구는 계열회사의 감사인이 주력회사의 감사인과 일치하는지 여부에 따라 그들의 감사품질이 차이가 있는지를 조사한다. 또한 계열사가 주력회사와 동일한 감사인을 선임하더라도 선임한 감사인의 규모 (Big4)에 따라 체계적인 차이가 존재하는지를 조사한다. 분석결과 계열회사가 주력회사와 동일한 감사인을 선임한 경우 그 감사품질은 상이한 감사인을 선임한 경우보다 유의하게 높다. 이는 주력회사와 그 감사인은 계열회사에 대한 정보를 종합적으로 수집하고 통제할 수 있으며, 특히 감사위험이 높은 내부거래에 대한 정보를 상세하게 파악하고 있기 때문에 주력회사의 감사인이 계열회사도 감사할 경우 계열회사의 감사품질이 높을 것이라는 해석과 일치한다. 동일한 감사인을 선임한 경우도 동일감사인이 Big4 여부에 따라 차이가 존재할 가능성을 조사한 결과 동일감사인을 선임하는 기업과 상이한 감사인을 선임하는 기업의 차이를 통제한 대응표본을 사용한 분석에서는 Big4 효과는 존재하지 않았다. 이는 동일한 감사인을 선임하는 계열사에서 감사인의 규모는 감사품질의 향상과 관련이 없다는 해석과 일치한다.

The main firm in large business groups as designated by the Fair Trade Commission can exercise a significant influence over almost all the important matters concerning the business group because it is located at the top of the entire business group. The auditor of the main firm, therefore, is likely to have access to related-firm transactions (i.e., internal business transactions between the main firm and other member firms and also among other member firms within the business group). This suggests that if the auditor of the main firm also audits the other member firms within the business group, he will be able to collect information and evidence about the internal transactions. Because of such information advantage relative to the case that the main firm and the other member firms have different auditors, it is reasonable to expect that the audit quality of the other member firms will be higher if both the main firm and the other member firms have the same auditor. We examine whether the audit quality of the other member firms when both the main firm and the other member firms hire the same auditor is systematically higher than that when they hire different auditors. In addition, we investigate whether the systematic differences, if any, vary according to auditor size (i.e., Big4 versus non-Big4). The results reveal that the audit quality is significantly higher if the main firm and the other member firms have the same auditor than they have different auditors. This is consistent with the argument that due to the informational advantage such as an easy access to the internal transactions between the main firm and the other member firms within the business group, the audit quality of the auditor of the other member firms who also is the auditor of the main firm will be higher than that of the auditor who does not audit the main firm. When the sample is divided on the basis of the auditor size of the other member firms, the results from the univariate analysis and the multivariate regression analysis with no client firm matching analysis indicate that the audit quality of the member firms is higher when the main firm and the other member firms have the same Big4 auditor than when they have non-Big4 auditors. However, when the firm characteristics of the member firms that hire the same auditor and a different auditor are matched by year, listing status, two-digit industry, asset size, and return on assets, the Big4 effect no longer exists, suggesting that the Big4 effect from the univariate analysis and he multivariate regression analysis with no client firm matching analysis is likely to be a different representation of the client effect. Self-selection is a concern in auditor selection research including our work. In order to alleviate this concern, we match sample firms with potential control firms using industry and prior period operating performance and redo the analysis. However, the results remain qualitatively unaltered, suggesting that our finding is unlikely to be driven mainly by selection bias. When audit quality is proxied by performance matched discretionary accruals, the results remain qualitatively similar.