1. Determine sample size.

Please specify the sample error you would like to accept and the confidence level (Z score =1.95 if confidence level is 95%, Z score =2.56 if confidence level is 99%). The commonly used confidence level is 95%. The Sample error is correlated with the sample size if the standard deviation is fixed. That means the smaller the sampling error you request, the larger the sample size will be.

When you calculate the sample size, you can give a range correspondent to a certain sampling error.

There are several rules that you may want to follow such as the minimal sample size should be 100. You can use 10% of the population as long as the population size is less than 10,000. You can also use the following table to select your sampling error and sample size.

Size of population Margin of error >5000 5000 2500 1000 500 200 +10% 96 94 93 88 81 65 17.5% 171 165 160 146 127 92 +5% 384 357 333 278 217 132 13% 1067 880 748 516 341 169