2. Sample size
a. The sample size for an attribute test depends on the following four factors:
1) The confidence level is the percentage of times that a sample is expected to be representative of the population. The greater the desired confidence level, the larger the sample size should be.
a) For a test of the controls, the confidence level is the complement of the allowable risk of overreliance on the control. For example, if this risk is 5%, the confidence level is 95% (100% -5%).
2) The population size is the sum of the items to be considered for testing. The larger the population size, the larger the sample size should be.
a) However, for a very large population, the population size has a small effect on the sample size. Above a certain population size, the sample size generally does not increase.
3) The expected deviation rate (expected rate of occurrence) is an estimate of the deviation rate in the current population
a) The greater the population deviation (variability in the population), the larger the sample size should be.
4) The tolerable deviation rate (desired precision) is the highest allowable percentage of the population that can be in error (noncompliance rate) and still allow the auditor to rely on the tested control.
a) The lower the tolerable deviation rate, the larger the sample size should be