Factors in Determining Sample Size Contents Questions Involving Means. Questions Involving Proportions. Determining Level of Precision After Data Collection. Questions Involving Means Three factors are required to specify sample size a. The standard deviation of the population. More the standard deviation, larger sample size is required (S) b. The magnitude of acceptable error ( i.e plus or minus some amount). Less the error, larger sample Size is required ( E) c. The confidence level ( i.e. 90%, 95% or 99%). More the confidence interval, larger the sample size required.(Z) Estimating S: 1. It is expected to be about one sixth of the range. eg. if we expect the price range to be 100 to 700, the standard deviation will be 700-100=600, 600 divided by 6 will be about 100. 2. You can find the standard deviation with the help