Clinical trial databases are usually audited prior to database lock to assure that the data meet certain desired quality levels. The audit can be conducted based on either all data items in the database or samples of data items. If samples of data items are audited, issues of type I and type II errors arise and sample size determination becomes crucial in controlling these errors. In this paper, we discuss the statistical issues relating to data audit, focusing on how to control type I and type II errors. Formulas for sample size determination are proposed, procedures for conducting data audit are recommended, and different sampling schemes are discussed.
