ABSTRACT
In order to give every individual an equal chance, you will need to know the identities of each one of them as well as how to contact them (e.g., an address). Often, researchers have this knowledge for only a subset of the population of interest. This is called the sampling frame, that is, the set of individuals accessible to a researcher. For example, suppose your research purpose calls for contacting all students who have graduated from a school during the past 10 years. You will probably find that the alumni records (with current addresses) are incomplete because the alumni office has lost contact with many of the graduates. Thus, your sample will need to be drawn from the subset for which current addresses are available. The following example shows how this might be proposed.
