SAMPLING

Sampling Techniques



Sampling Techniques

Sampling

Sampling occurs when researchers examine a portion or sample of a larger group of potential participants and use the results to make statements that apply to this broader group or population. The extent to which the findings of the research can be generalized to the larger group or population is an indication of the external validity of the design of research. Selecting a sample is an integral part of designing sound research.

An awareness of the principles of sampling design is imperative to the development of research with strong external validity. In theory, a sound sampling method will result in a sample that is free from bias (every individual has a equal chance of being selected from the population) and is reliable (a sample will yield the same or comparable results if the research were repeated).

A sample that is free from bias and reliable is considered as the real representative of the selected population of interest. A representative sample adequately reflects the properties of interest of the population being examined, thus enabling the researcher to study the sample but draw valid conclusions about the larger population of interest. If the sampling procedures are flawed, then the time and effort put into data collection and analysis can lead to erroneous inferences. A poor sample could lead to meaningless findings based on research that is fundamentally flawed. Researchers use sampling procedures to select units from a population. In social science research, the units being selected are commonly individuals, but they can also be couples, organizations, groups, cities, and so on.

Steps in the Sampling Process

The sampling process can be diagrammed as shown in Figure 1. Identifying the population or entire group of interest is an important first step in designing the sampling method. This entire population is often referred to as the theoretical or target population because it includes all of the participants of theoretical interest to the researcher. These are the individuals about whom the researcher is interested in making generalizations. Examples of possible theoretical populations are all high school principals in the United States, all couples over age 80 in the world, and all adults with chronic fatigue syndrome. It is hardly ever possible to study the entire theoretical population, so a portion of this theoretical population that is accessible (the accessible population or sampling frame) is identified. Researchers define the accessible population/sampling frame based on the participants to which they have access. Examples of accessible populations might be the high school principals in the state of Colorado, couples over age 80 who participate in a community activity targeting seniors, or patients who have visited a particular clinic for the treatment for chronic fatigue syndrome. From this accessible population, the researcher might employ a sampling design to create the selected sample, which is the smaller group of individuals selected from the accessible population. These individuals are asked by the researcher to participate in the study. For example, one might sample high school principals by selecting a random sample of ...