In this study we investigate whether the characteristics of clients, auditors, and the auditor‐client relationship simultaneously determine audit and non‐audit fees. As done in prior studies, we maintain that fees proxy for the level of service provided and follow the physical flow of knowledge. Estimating single‐equation models of audit and non‐audit fee models, we confirm prior findings of an association between audit and non‐audit fees. Studies conclude that such evidence is consistent with knowledge spillovers between the two services. However, we document empirically that audit and non‐audit fees are simultaneously determined. Because the data indicate audit and non‐audit fees are jointly determined, we then investigate whether previously documented associations between audit and non‐audit fees are the result of biased estimation induced by using endogenous variables in single‐equation models. In contrast to results from single‐equation estimations, we find no association between audit and non‐audit fees using a simultaneous specification of the fee system, suggesting that single‐equation estimations suffer from simultaneous‐equations bias. In sum, the findings are not consistent with the existence of economies of scope from the joint performance of audit and non‐audit services after controlling for the joint behavior of audit and non‐audit fees. Given the ongoing debate over the level of allowed non‐audit services by auditors, the argument for the joint provision of audit and non‐audit services is less justified than if joint‐supply benefits had been documented.

This study examines the association between audit committee characteristics and the ratio of nonaudit service (NAS) fees to audit fees, using data gathered under the Securities and Exchange Commission's (SEC's) fee disclosure rules. Issues related to NAS fees have been of concern to practitioners, regulators, and academics for a number of years. Prior research suggests that audit committees possessing certain characteristics are important participants in the process of managing the client‐auditor relationship. We hypothesize that audit committees that are independent and active financial monitors have incentives to limit NAS fees (relative to audit fees) paid to incumbent auditors, in an effort to enhance auditor independence in either appearance or fact. Our analysis using a sample of 538 firms indicates that audit committees comprised solely of independent directors meeting at least four times annually are significantly and negatively associated with the NAS fee ratio. This evidence is consistent with audit committee members perceiving a high level of NAS fees in a negative light and taking actions to decrease the NAS fee ratio.