6. To project the frequency of shipments to wrong addresses, an internal auditor chose a random sample from the busiest month of each of the four quarters of the most recent year. What underlying concept of statistical sampling did the auditor violate?
A. Attempting to project a rate of occurrence rather than an error rate.
B. Failing to give each item in the population an equal chance of selection.
C. Failing to adequately describe the population.
D. Using multistage sampling in conjunction with attributes.
ANSWER (B) is correct.
REQUIRED: The concept of statistical sampling violated by sampling from the busiest month.
DISCUSSION: A random sample is one in which every item in the population has an equal and nonzero chance of being selected for the sample. Here, the auditor deliberately excluded shipments from the slower months.
Answer (A) is incorrect. Randomness is not associated with a rate of occurrence (often referred to as an error rate).
Answer (C) is incorrect. The population is adequately described as the four quarters of the most recent year.
Answer (D) is incorrect. Multistage sampling is appropriate when homogeneous subpopulations can be identified and sampled from; sample items are then selected from the randomly selected subpopulations.