Is it acceptable to use the same set of transactions and the same sample size to test two different controls?

Question

Evaluate the appropriateness of Darrell’s conclusions relating to the first two controls:

Answer 1

Auditors often establish one sample size for all controls tested within a business process. This is efficient
because each transaction often passes through all of the controls, and the auditors can test all of the
controls with the same sample. However, the attribute sample size table in the case is designed to
provide a sample size such that if the sample yields a deviation rate of what we expect or lower, then
we will have achieved our audit objectives. Conversely, if we find a misstatement rate higher than
we expected, then we generally will not meet our objectives (i.e., sample size too small to provide
sufficient assurance and/or deviation rate greater than we can tolerate).
When an auditor selects one sample size to test multiple controls, he or she needs to determine
which sample size is appropriate. Normally the auditor should use the largest of the sample sizes
suggested based on the expected and tolerable deviation rates. In this case, the sample size table in
Appendix A suggests that a sample size of 58 is appropriate for the first control, but the higher expected
deviation rate for the second control means that a larger sample size is necessary (77). Therefore,
Darrell should have selected a sample of 77 items rather than 58.