StATS: What is a sample?

A subset of a population. A random sample is a subset where every item in the population has the same probability of being in the sample. Usually, the size of the sample is much less than the size of the population. The primary goal of much research is to use information collected from a sample to try to characterize a certain population. As such, you should pay a lot of attention to how representative the sample is of the population. If there are problems, with representativeness, consider redefining your population a bit more narrowly. For example, a sample of 85 smokers between the ages of 13 and 18 in Rochester, Minnesota who respond to an advertisement about participation in a smoking cessation program might not be considered representative of the population of all teenage smokers, because the participants selected themselves. The sample might be more representative if we restrict our population to those teenage smokers who want to quit.

This page was written by Steve Simon while working at Children's Mercy Hospital. Although I do not hold the copyright for this material, I am reproducing it here as a service, as it is no longer available on the Children's Mercy Hospital website. Need more information? I have a page with general help resources. You can also browse for pages similar to this one at Category: Definitions, Category: Hypothesis testing.