Populations and Samples

Fundamentals of Social Statistics by Adam J. McKee

Social science research usually begins with a question about a specific group of people.  In the language of research, the entire group of people that a researcher is interested in is called a population.

A population is the group of all the people of interest in a particular research study.

Many times, populations are large.  A political scientist, for example, may be interested in every registered female voter in the United States.  Sometimes, however, populations can be very small, such as when a study concerns a very small group, such as female Supreme Court justices.

A population does not always have to consist of individual people.  It can be groups of people, such as a population of police departments.  A population can also consist of animals, or non-living things, such as the production of a factory.  A population can be anything an investigator wants to study.

Research questions are concerned with the whole population, but it is seldom feasible to collect data from an entire population.  For this reason, researchers usually select a small group from among the population and limit their study to those individuals in the smaller group.  This set of individuals selected from the population is called a sample.  A sample is intended to be representative of the population from which it was drawn.  That is, the sample should be just like the population in every way that is important to the study.

A sample is a group of individuals selected from a population that serves to represent the population in a research study.

If your physician thinks you may be anemic, she may draw a sample of your blood to test your iron level.  You would be upset if the doctor wanted to take out all of your blood to be tested!  A sample is just fine so long as the blood taken out of your body is just like the blood remaining in your body.  If this is the case, then we can say that the sample of blood is representative of all your blood—the population of blood.  With blood, representativeness can be taken for granted.  When it comes to selecting a group of people to represent a larger group, we have to take great care to make sure that the sample of people is a representative sample.

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Last Modified:  02/03/2021

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