Auditor Market Power and Audit Quality Revisited: Effects of Market Concentration, Market Share Distance, and Leadership

This study examines whether auditor market power is associated with audit quality. Regulators around the world have repeatedly expressed concerns about the high levels of supplier concentration, the limited number of audit suppliers in the audit market, and the potential adverse consequences of their (alleged) market power. Using U.S. data from 2009 to 2017, we examine the effect on audit quality of two competing measures of auditor market power: (a) a "traditional" market concentration measure (Herfindahl index) and (b) a competing measure derived from spatial competition theory (i.e., market share distance from the closest competitor). Following Aobdia, we infer audit quality from two measures of financial reporting quality: (a) the level of absolute abnormal accruals, and (b) the incidence of financial statement restatements. Our results indicate that industry market share distance is positively associated with audit quality, but we do not find an association between market concentration and audit quality. In addition, we find that the positive association between market share distance and audit quality only holds when the incumbent auditor is a market leader, although industry leadership itself is not significantly associated with audit quality. These findings suggest that audit quality is positively affected by a market leader's industry market share dominance over its competitors rather than by industry specialization per se. JEL Classification: M4; L0