Auditing is performed by the auditor in accordance with a written audit plan and procedures, and involves the examination and evaluation of information obtained through investigation of the audit trail (e.g. essential documents and SOPs) and a trial site(s) (e.g. facilities and equipment), as well as interviews with the auditee, etc. It is important to specify reference documents that auditees comply with before performing an audit so as to ensure fair conduct of audit. The auditor evaluates conformity and compliance with these reference documents. The auditor should inform the sponsor about the conduct of an audit in advance.