6. Conclusion
Audit fees and auditor’s opinion have been
studied by many researchers to see whether
economic dependence will impair auditor’s
independence; however, the results are inconclusive.
The current research study attempts to answer this
research question in Thailand by measuring audit
fees in each type of opinions. Research results
reveal that firms with modified auditor’s opinion pay
higher audit fees than those with clean auditor’s
opinion. The mean difference in audit fees is
significant for firms with clean opinion and those with
unqualified opinion with explanation and qualified
opinion. This evidence implies that when audit clients
have uncertainties and unresolved issues, auditors
have to perform more audit works in order to obtain
sufficient and appropriate audit evidence.
Consequently, auditors are likely to issue modified
auditor’s opinion to avoid reputation and litigation
risk and charge high audit fees to their clients to
compensate with their additional costs. In other
words, high audit fee may represent high audit
quality since auditors work harder in audit
engagement with uncertainties and unsolved issues.
When considering the difference in audit fee by
opinion types and by size of audit firms, the result is
qualitatively similar to the first finding. Big 4 and
non-Big 4 clients with modified opinion pay higher
audit fees than those with unqualified opinion. Big 4
and non-Big 4 audit clients pay significant higher
audit fees for clean opinion with explanation and
qualified opinions than for clean opinion. The result
shows that economic dependence or high audit fee
does not impair auditor’s independence for both of
Big 4 and non-Big4 auditors in expressing modified
opinions. Besides, high audit fee may represent
greater audit effort and more audit quality. Audit fee
for disclaimer of opinion is similar to that for clean