Samples and Sampling
The term “sampling,” as used in research, refers to the process of selecting the individuals who will participate (e.g., be observed or questioned) in a research study. A sample is any part of a population of individuals on whom information is obtained. It may, for a variety of reasons, be different from the sample originally selected. Samples and Populations
The term “population,” as used in research, refers to all the members of a particular group. It is the group of interest to the researcher, the group to whom the researcher would like to generalize the results of a study. A target population is the actual population to whom the researcher would like to generalize; the accessible population is the population to whom the researcher is entitled to generalize. A representative sample is a sample that is similar to the population on all characteristics.
Two-stage random sampling A process in which clusters are first randomly selected and then individuals are selected from each cluster. Stratified random sampling The process of selecting a sample in such a way that identified subgroups in the population are represented in the sample in the same proportion as they exist in the population. Random sampling Methods designed to select a representative sample by using chance selection so that biases will not systematically alter the sample. Cluster random sampling The selection of groups of individuals, called clusters, rather than single individuals. All individuals in a cluster are included in the sample; the clusters are preferably selected randomly from the larger population of clusters.
Random Sampling Methods
A simple random sample is a sample selected from a population in such a manner that all members of the population have an equal chance of being selected. A stratified random sample is a sample selected so that certain characteristics are represented in the sample in the same proportion as they occur in the population. A cluster random sample is one obtained by using groups as the sampling unit rather than individuals. A two-stage random sample selects groups randomly and then chooses individuals randomly from these groups. A table of random numbers is a table of numbers, listed and arranged in no particular order, that is used to select a random sample.