Final answer:
The tolerable deviation rate results in the greatest decrease in sample size in attribute sampling for a test of controls because a higher tolerable rate allows auditors to accept more deviations without affecting the audit conclusion.
Step-by-step explanation:
The question revolves around identifying which factor will result in the greatest decrease in sample size when testing controls in auditing. Among the options provided are desired confidence level, tolerable deviation rate, and expected population deviation rate. To answer the question: Increasing the desired confidence level typically increases the sample size because more assurance is required from the sample. Conversely, increasing the tolerable deviation rate allows for more errors before the control is considered ineffective, which can reduce the sample size. However, increasing the expected population deviation rate suggests that errors are more common in the population, which means a larger sample might be needed to adequately assess the control.
Therefore, the tolerable deviation rate B. option given here is what results in the greatest decrease in sample size for an attribute sample in a test of controls. If the tolerable rate of deviation is increased, auditors can accept a higher level of deviation before determining that controls are not effective, allowing for a smaller sample to be tested without diminishing the effectiveness of the audit test.