If the auditor has more assurance or intends to obtain more assurance from accounting and internal control systems, it means his assessment of control risk is low and for this reason a larger sample size will be needed. This is because the auditor needs to gather more audit evidence to support his assessment of control risk.
ii) Tolerable Error
This refers to the rate of deviation from the prescribed control procedure the auditor is willing to accept. The lower the rate of deviation the larger the sample size needs to be.
iii) Expected Error
This is the rate of deviation from the prescribed control procedure the auditor expects to find in the population. The higher the expected error, the larger the
sample size needs to be so that the auditor can be in a position to make a reasonable estimate of the actual rate of deviation.
iv) Confidence Level Required by Auditor
The greater the degree of confidence that the auditor expects/requires that the results of the sample are in fact indicative of the actual incidence of error in the population, the large the sample size needs to be.
v) Number of sampling units in the population
This factor mostly affects small businesses, where population is likely to be small. For large populations, the actual size of the population has very little effect on sample size. However when population is small, audit sampling may not be as efficient as alternative means of obtaining sufficient appropriate audit evidence.