本研究旨在探討營運多角化對於公司盈餘品質之影響以及當主查會計師因無法直接查核重大轉投資公司而出具分擔責任之查核意見時，是否會使多角化公司之盈餘品質趨於惡化。本研究區別跨國多角化與產業多角化兩種型態，並提出兩組互競假說─資訊不對稱假說與應計數抵銷假說。研究結果發現，對於主查會計師出具分擔責任意見之受查公司，若其跨國多角化程度愈高，則其應計數品質愈差，但產業多角化對於應計數品質並無顯著的不利影響。此外，若主查會計師可以直接查核所有重大轉投資公司而出具無保留意見，則跨國多角化對於應計數品質之負面影響會趨於緩和。本研究結果顯示，跨國多角化程度高且重大轉投資公司未經主查會計師查核之公司，負面之資訊不對稱效果凌駕了正面之應計數抵銷效果，其盈餘品質堪虞。再者，有效外部審計之監督力量以及產業多角化之應計數抵銷效果，均有助於減緩跨國多角化對於應計數品質之負面影響。

We examine whether corporate diversification deteriorates earnings quality and whether the audit scope limitation due to material subsidiaries or affiliate investments not audited by the principal auditor (as proxied by shared audit opinion) exacerbates the earnings quality problem for diversified firms in Taiwan. We make an explicit distinction between global diversification and industrial diversification. We find that after controlling the level of industrial diversification, greater global diversification deteriorates accruals quality for diversified firms that receive shared audit opinions. However, the adverse effect of global diversification on accruals quality will be mitigated if the principal auditor of diversified firms can directly audit all material subsidiaries or affiliated companies (as proxied by standard unqualified audit opinion). There is weak evidence which shows that after controlling the level of global diversification, greater industrial diversification may ameliorate the accruals quality problem for diversified firms receiving shared opinions. Our study suggests that the unobservability of material foreign subsidiaries or affiliate investments by the principal auditor impairs the audit quality and provides empirical support for recent regulatory reforms to enhance the transparency of financial disclosure and strengthen the auditors' responsibilities for globally diversified firms.