Samples and Populations

What is a Sample? 

Most people, we think, base their conclusions about a group of people (students, actors, football players and so on) on the experiences they have with a fairly small number or sample of individual members. One of the most important steps in the research process is the selection of the sample of individuals who will participate (be observed or questioned). Sampling refers to the process of selecting these individuals. 

Samples and Populations 

A sample in a research is the group on which information is obtained. The larger group to which one hopes to apply the results is called the population. 

Example:

All 700 students at State University who are majoring in mathematics, constitute a population; 50 of those students constitute a sample. Students who own automobiles make up another population, as do students who live in the campus dormitories. Notice that a group may be both a sample in one context and a population in another context. All State University students who own automobiles constitute a sample of all automobile owners at state universities across the Unites States. 

When it is possible, researchers would prefer to study the entire population of interest. Most populations of interest are large, diverse and scattered over a large geographic area. 

Defining the Population 

The first task in selecting a sample is to define the population of interest. In what group, exactly is the researcher interested? To whom does the results of the study to apply? Below are some examples of population. 

• All high school principles in the United States
• All students attending Central High School in Omaha, during the academic year 2005-2006
• All students in Ms. Brown's third grade class at Wharton Elementary School

The above examples shows that a population can be any size and that it will have at least one or several characteristic(s) that sets it off from any other population.