Stratified mean per unit sampling is a method of audit sampling that divides the population into subgroups (strata) based on some characteristic, such as monetary value, and then selects a sample from each stratum using mean per unit sampling. Mean per unit sampling is a method of audit sampling that estimates the total value of a population by multiplying the average value of the sample items by the number of items in the population. Stratified mean per unit sampling is suitable for populations that have a high variability or a skewed distribution, such as the bank accounts in this question. By stratifying the population, the auditor can reduce the sampling error and increase the precision of the estimate.
Difference estimation sampling (option A) is not the best sampling approach for these accounts. Difference estimation sampling is a method of audit sampling that estimates the total error or misstatement in a population by multiplying the average difference between the book value and the audited value of the sample items by the number of items in the population. Difference estimation sampling is suitable for populations that have a low variability and a symmetrical distribution, which is not the case for the bank accounts in this question.
Customer unit sampling (option C) is not a sampling approach, but a type of monetary unit sampling.
Monetary unit sampling is a method of audit sampling that selects sample items based on their monetary value, rather than their physical units. Customer unit sampling is a variation of monetary unit sampling that treats each customer account as a single unit, regardless of how many transactions or balances it contains. Customer unit sampling may be appropriate for testing existence or occurrence assertions, but not for estimating total values.
Unstratified mean per unit sampling (option D) is not the best sampling approach for these accounts.
Unstratified mean per unit sampling is a method of audit sampling that applies mean per unit sampling to the entire population without dividing it into subgroups. Unstratified mean per unit sampling may result in a larger sample size and a lower precision than stratified mean per unit sampling, especially for populations that have a high variability or a skewed distribution, such as the bank accounts in this question.
Therefore, option B is the correct answer.
References:
* Audit Sampling - AICPA
* Audit Sampling: Examples and Guidance To The Sampling Methods
* Audit Sampling | Audit | Financial Audit - Scribd