In statistics, two of the most important concepts are populations and sample sizes. A study needs an adequate sample size to mean anything. For example, a study could say that a baseball player who hits two home runs at four at bats in a game hits a home run 50 percent of the time. This sample size is too small to be meaningful. Thus, population size is crucial as it defines what the study is looking at as a whole.

Write out the fact of the study. For example, a statistician studies the effects of health food on high school students in a small town. The statistician studies 40 students at a high school of 250.

Determine the total population of the study. The population will always be the bigger number of the sample size and population. The population is the whole group of people being studied. In the example, the population is the size of the high school being studied, so 250 people.

Determine the sample size of the study. The sample size is the number of people who the statistician examines. In the example, the statistician examined 40 students, so the sample size is 40 people.