Click the Survey System link (see Resources) and scroll down to Sample Size Calculator. The calculator will figure out how many people are needed to survey in order to accurately reflect the population. The calculator works with two confidence levels: 95 percent and 99 percent. However, you can input your own confidence interval and population size, if known.
Click the Raosoft link (see Resources). The calculator offers three confidence levels: 90 percent, 95 percent, and 99 percent. Input the margin of error, or confidence interval, and the population size. This calculator is a good choice for the beginning students because it offers explanations for all of the choices in case there is confusion about what a confidence level or margin of error is. Once the data is entered, the calculator will return the minimum number of people needed to sample and provides a selection of alternate scenarios for the data.
Navigate to Macorr's Sample Size Calculator (see Resources). The basic interface has options for three confidence levels and varied confidence intervals and populations. Find explanations for each term by clicking the "?" button next to each text box or drop down menu. Work with the calculator online or download it to a computer.