In auditing, sampling is an inevitable means of testing. However, sampling is always associated with sampling risks which auditors have to control.
Sampling risk represents the possibility that auditor's conclusion based on a sample is different from that reached if the entire population were subject to audit procedure. The auditor may conclude that material misstatements exist, in fact they do not; or material misstatements do not exist but in fact they do exist. Auditor can lower the sampling risk by increasing the sampling size.
Non-sampling risk includes factors that cause auditors to reach a conclusion other than the sampling size. Misinterpretation of evidence and inappropriate procedures are good examples. Changing of the sampling size would not reduce non-sampling risk.