Measuring audit quality has also been a controversial issue in academics for quite
some time (Bing et al., 2014). In their review of archival audit research, DeFond and
Zhang (2014) note that audit quality is generally difficult to measure due to the amount
of assurance auditors provide being unobservable. However, the literature has used
auditor size as a proxy for audit quality because large auditors are expected to have
stronger incentives and greater competencies to provide high audit quality. Using Big 4
firms as an indicator of audit quality has been one of the most thoroughly researched
areas in the literature, and it provides comprehensive evidence that Big 4 auditors tend
to deliver higher audit quality (DeFond and Zhang, 2014).