20. When an internal auditor uses monetary-unit statistical sampling to examine the total value of invoices, each invoice
A. Has an equal probability of being selected.
B. Can be represented by no more than one monetary unit.
C. Has an unknown probability of being selected.
D. Has a probability proportional to its monetary value of being selected.
ANSWER (D) is correct.
REQUIRED: The effect of using monetary-unit sampling to examine invoices.
DISCUSSION: Monetary-unit sampling, also called probability proportional-to-size sampling, results in the selection of every nth monetary unit Thus, a US $1,000 item is 1,000 times more likely to be selected than a US $1 monetary unit item. The probability of selection of a sampled item is directly proportional to the size of the item.
Answer (A) is incorrect. Each monetary unit, not each invoice, has an equal probability of being selected (unless all invoices are for the same amount).
Answer (B) is incorrect. It is possible for two or more monetary units to be selected from the same item; e.g., a US $4,500 item will be represented by four monetary units if every 1,000th dollar is selected.
Answer (C) is incorrect. The probability of selection can be calculated using the monetary value of the item and the monetary value of the population.