Why can traditional variable sampling prevent underestimation?

The unit mean method is a variable sampling method to estimate the total value through the unit mean of samples.

Average sample = actual sample size/sample size

Estimated total = sample average × total size

Inferred misstatement total = estimated actual total-book total

2. Difference estimation method is a variable sampling method to infer the difference between the overall record value and the audit value through the difference between the sample record value and the audit value, and then evaluate the overall record value.

Average misstatement = the difference between the actual number of samples and the book number/sample size

Inferred overall misstatement = average misstatement × overall size

3. Ratio estimation method is a variable sampling method to infer the ratio of the overall audit value to the recorded value through the ratio of the audit value to the sample recorded value, and then estimate the overall audit value and evaluate the correctness of the original recorded value.

Ratio = sample approved amount/sample book amount

Estimated actual total amount = total book amount × ratio

Inferred misstatement total = estimated actual total-book total