4-I agree with you that Sampling theory was developed to determine the most effective way of acquiring a sample that accurately reflects the population under study. A sample is the selected group of people or elements in a study. The sample selected should represent an identified population or a particular group of individuals or elements that is the focus of the research. Sampling Theory – Analysis of Health Surveys Assignment Papers.
And to add that Sampling theory is also the study of the relationship that exist between a target population and the samples that are drawn from the population and this only applies to samples that are drawn randomly. The main concepts of the sampling theory are the target population, representative samples and sampling plans or methods.