Scientific research starts with a general research question on a specific group of individuals. For example; a researcher wants to know about the effect of divorce on children's self-esteem or to examine the political attitudes that are applied to women and men. In the first case, the research is interested in children of divorced families and the secondary concern is women and men. As in these examples, the entire group of subjects that a researcher would like to study on is called the population. In some cases, the population of the study may be too large. Like the men and women in the world that was mentioned in the second example. In such limited cases, researchers can sort out a specific population: as women and men living in Turkey. In this example, the population living in Turkey can be limited from a great size of the group to a smaller one to suggest the researchers studying on women and men in the public servant. Moreover, the population does not necessarily have to be a person. In some studies the population can consist of animals, companies, a department or a product of a company, depending on the research subject.
Although the research question covers the entire population, usually it is impossible for researchers to examine every individual in the population. For this reason, smaller and more accessible groups are selected from the population as the research group, and the study is limited to the individuals in the selected group. This new smaller group, that selected from the population, is in the statistical term called sample. In other words; a sample is a group that is selected from the population and considered to represent the population in a scientific research.