IAASB auditing standards use professional code of ethics issued by International Ethical Standards Board of Accountants (IESBA) to describe the ethical requirements for conducting an audit. However, accountancy bodies all over the world have their own ethical standards for their members working as accounting and auditors.
One common requirement in every ethical standard is that auditor must be objective in everything he do especially while making up his opinion about anything during an audit engagement he should not let go objectivity. Objectivity basically requires auditor to be rational in opinion and decision making and being rational means using facts to back up the decisions instead of liking and disliking. This ultimately ensures that audit is free from any bias.
So, we understood that to stay objective auditor needs to gather information which he is going to use to reach conclusions and then such conclusions make up auditor’s opinion. And this is not only the requirement of auditing standards but also of code of ethics applicable to auditor under given circumstances.
There are no mandatory requirements or benchmarks provided anywhere in auditing standards or elsewhere that suggests the amount of audit evidence that is needed to be obtained by the auditor. How much information is necessary to make up an audit opinion depends on auditor’s professional judgment i.e. auditor has to decide about the amount of audit evidence to be gathered in which lot of factors are involved. And due to same factors which are very important, auditor needs to exercise his professional judgment.
It is so important from the point of view of conducting and completing an audit engagement satisfactorily that without sufficient appropriate audit evidence auditor will not be in a position to express his opinion.