Why is there a need of external experts' opinion on various technical matters to auditors ?

An auditor may take external expert's opinion on various technical matters which forms the audit evidence. The auditor has to place reliance on the opinion expressed by the external expert considering his reliability, competency, consistency with data & information and independence. In case of an external expert it shall be ensured that the interests and relationship of the external expert does not constitute a threat to that expert's objectivity. The auditor shall evaluate adequacy of expert's work having regard to the following: Relevance and reasonableness of expert's findings/conclusions and consistency thereof with other audit evidence. Relevance and reasonableness of assumptions and methods used in the expert's work. Relevance, reasonableness, accuracy and completeness of source data (if any) used in the expert's work provided such data are significant for the expert's Work. Agreement with the expert on the nature and extent of further work by the expert in case expert's work is found to be inadequate for audit purpose. Performance of additional, appropriate audit procedures in case expert's work is found to be inadequate for audit purpose.