In parallel simulation, actual client data are reprocessed using an auditor software program. An advantage of using parallel simulation, instead of performing tests of controls without a computer, is that:

Choice "d" is correct. Use of computer assisted audit techniques typically allows a greater number of items to be tested at relatively little additional cost. For example, once the auditor has created the software program, it takes little effort to reprocess additional transactions. Manual tests, on the other hand, must be applied separately to each individual transaction, making it more costly to increase sample size. Choice "a" is incorrect. Reprocessing of actual client data may not include all types of transaction errors and exceptions. Only errors or exceptions in the actual data would be included. Choice "b" is incorrect. The client's computer personnel likely would be providing the actual client data, and so would have some knowledge of when the data was being tested. Choice "c" is incorrect. Neither manual testing nor parallel processing includes a risk of corrupting the client's data, since neither one of them affects the client's live data or files.