The major reason that the difference and ratio estimation methods would be expected to produce audit efficiency is that the
　　A. Beta risk may be completely ignored.
　　B. Calculations required in using difference or ratios estimation are less arduous and fewer than those required when using direct estimation.
　　C. Number of members of the populations of differences or ratios is smaller than the number of members of the population of book values.
　　D. Variability of the populations of differences or ratios is less than that of the populations of book values or audited values.
　　Answer:D
　　D is corrent because difference and ratio estimation methods measure the difference between audit and book values or the ratio of audit to book values. As these differences should not be great, the population of these differences will have little variance. In statistical sampling the less variation in a population, the smaller the required sample to provide an estimate of the population. In other words, difference and ratio estimation methods are more efficient because the differences between audit and book values are expected to vary less than the actual items in the population.
　　A is incorrect because beta risk can never be ignored, as beta risk is the risk of accepting an incorrect (unacceptable) population.
　　B is incorrect because the calculations required in difference and ratio sampling are similar to those used in direct estimation sampling.
　　C is incorrect because the number of members in the population for differences or ratio methods would be the same as the number of items in the population for a direct estimation method. In difference sampling, many items would be zero because audit and book values are the same, and in ratio sampling, many of the members would be one for the same reason.