## Key Terms

Confidence Level: A measure of how confident you are that your sample accurately reflects the population. Common standards used by researchers are 90%, 95%, and 99%.

Sample Size: The number of completed responses your survey receives is your sample size. It's called a sample because it represents a part of the total group of people whose opinions or behavior you care about. As an example, you can select at random 10 out of 50 employees from a department at your job. Those 10 are the sample and the 50 are the population.

The bigger the population is, the bigger the sample will need to be to accurately reflect the population.
See our sample size calculator for how to calculate your needed sample size.

Population Proportion: This can be described as the makeup of the population. For example, if it's well known 60% of college students are female you could say the population proportion of college students is 60% female. If you wanted to mainly get opinions of college females, you would use this 60 percent in the formula below (for P). Often these numbers are not known and 50% (.50) is used for P. This .5 number produces the largest possible sample size, as it is the most conservative estimate.

Population Size:This is the size of your total population. Often this will be an extremely large number (such as the number of people in the United States). If you do not know your population size, it will be assumed that is infinitely large, and margin of error will be calculated using the first equation blow. If you do know your population size, such all the employees at your workplace, the margin of error will be calculated using the second equation below.