Use an online sample size calculator. The sample size calculation method you have learned in Chapter 10 is universal, and you can find a great many free online sample size calculators that use it. if a researcher understands the underlying concepts of confidence level, margin of sample error, and variability, there is absolutely no need to do "hand" calculations to determine sample size. As an experiment, find an online calculator that requires you to enter in: Confidence Level, typically 95% or 99%; Confidence Interval, accuracy, or margin of error; Variability or population proportion (sometimes "fixed" at 50%); Population size.

Enter in the values typically associated with national opinion polls, namely 95% confidence level, 3% error, variability of 50%, and population of 200,000,000. What is the sample size? Next, change the error to 3.5% and then 5.0%. What are the sample sizes associated with each margin of error? Finally, change the confidence level to 99% and 90% for 3% error. How does a change in confidence level change the sample size?